ASTRO FINAL
A full solar cycle takes approximately _________ years
11
How long could the sun's mass power the Active galactic Nucleus for it has a L=10^38 W?
11 Years
Speed of light, Second, month, year
1 Light Second = Distance light travels in 1 second 1 Light month= Distance light travels in 1 month 1 Light Year= Distance light travels in 1 year = 3x10^9 m/s*365 d/y*24 h/d *3600 d/h= 9.5 Trillion km
Sun Spot Cycle
11 years and every 11 years the magnetic field switches
What is the local solar time when the sun crosses your meridian?
12 noon
You notice a third quarter moon setting on the western horizon. What is the time?
12:00 noon
If you are in Cape Town at 12 noon local solar time, what would be the time on your watch?
12:48
The sun crossed the meridian at
12pm NOON
Solar Constant of Earth
1400 w/m2 , We receive 1400 Joules per second per m2 from the sun
If a 1m telescope takes 1 hour to get an image of a particular object, how long would it take a 5m telescope to take an image of the same object to the same quality?
60 mins / 25 = 2.4 mins on a 5 m telescope while 1 hour on 1 m telescope
The Kuiper belt
A region of the solar system that is just beyond the orbit of Neptune and that contains small bodies made mostly of ice
sedimentary rock
A type of rock that forms when particles from other rocks or the remains of plants and animals are pressed and cemented together
Why do the stars appear to move across the sky?
Diurnal motion = daily motion of sun and stars across the sky - The earth spins on its axis which makes the stars & sun appear to move across the sky daily
Gravitational Learning
Distortions in the shapes of background objects due to gravitational lensing by a massive foreground cluster: - Using the observations, astronomers can model the mass distribution in the foreground cluster and estimate how much dark matter there must be to cause the observed lensing effects - Measure how much mass is needed to distort the picture
Magma
Molten Mantle Rock, called lava when ejected from a volcano
the most geologically active body in the Solar System
Moon Lo, Jupiter
Daughter/ fission theory
Moon originated from Earth, when it was molten and spinning fast it might ejected some matter (e.g. from the pacific basin) But unlikely... because the Earth would have been spinning fast enough, and simulations cannot get the moon into a stable orbit
Hubble- Lemaitre Law plotting
Plotting the relationship between recessional velocity and distance to galaxies shows the following:
Zenith
Point in the sky directly overhead (altitude=90 degrees)
Gregorian Calendar
Pope Gregory XII set the calendar so that the vernal equinox fell on march 22nd. & changed the rules of a leap year.
condensation theory (The modern theory of planet formation)
Premise that stars and planets accumulate from contracting, accreting clouds of galactic gas, dust, and debris. Warms gas would form clumps and become planets of their own
Why do massive stars live for shorter times on the Main Sequence?
Their high masses mean stronger gravity and more gravitational energy hear the star to higher temperatures which causes the nuclear reactions to proceed much faster, use up fuel, and then evolve off the main sequence
Roche lobe
The volume of space a star controls gravitationally within a binary system.
How do we measure the density of the universe?
Try summing up the mass in galaxy cluster +dark matter and dividing by volume - Omega zero, the critical perimeter- very small --- Low density, Open universe Dark Matter = omega zero ~.25 -- But these are local measurements at particular places in the universe
Wien's Law (1897)
The wavelength of peak emission, is inversely proportional to the temperature of an object Wave Length Peak = 2.9 [mm]/T [K]
Star density increases
Dramatically towards the center of the galaxy - Star density is 10 million times higher than in solar neighborhood
A useful standard candle must:
Have a well defined luminosity - be bright enough to be observed at very large distance good example: Super Novae (carbon core) Type I - They all have very similar properties and very similar luminosities
The first stars that formed in the Milky Way now
Have random Orbits in the halo
Mercury's magnetic field
Magnetic field is 3x stronger in North than in South! - The other terrestrial planet to have a magnetic field. - part of the core musict be liquid to generate magnetic field
Average Gas speed
v(esc) > 6x
retrograde
moving backward
The galactic distances used to measure the acceleration of the Universe are determined by:
observations of exploding white dwarfs
Regolith
"lunar soil"; made from micrometeorite impacts; creates a fine "sand blasting" effect due to the absence of an atmosphere
If only 70% of the incoming solar energy makes it through the atmosphere to the Earth's surface, how energy would a sun-bather's body receive on a clear day on Clifton beach? Can assume the typical area of an average person's body is ~0.5m^2
(1400 w/m^2) x(0.7) x(0.5 m^2) = 490 W
You are somewhere on Earth at night. You look up and notice that the constellation Scorpius (RA 16h 53m, Dec -27) is directly overhead... (A)What is the Sidereal Time? (B)What is the latitude on earth?
(A)16 hours and 53 min - Same as the right ascension (B)27 Degrees South
Bootstrapping
- Distance Measurements Distance estimate of higher rungs in the ladder depends on estimates from the lower rungs
A star has the coordinated RA: 9h and Declination -41 degrees at the zenith. and the waxing present moon is setting. (a) What is the latitude of the ship at is current position? (b) What is the sidereal time when the researcher makes the observations? (c) The time on the Cap Town solar clock is 19:56. What is the longitude of the ship?
(a) Latitude is -41 degrees south (Declination is latitude) (b) The waxing present sets at 9pm, so it is 9pm (c) The longitude is 135 degrees East - If number is greater than 180 degrees = West - If number is less than 180 degrees= East Steps for C - Convert right ascension into a decimal - Multiple the time by 15 degrees - If you get a number greater than 180 degrees Then subtract 360 degrees to get your final answer
(a) Which stars would have the same absolute magnitudes? Explain why. [2 marks] (b) Which stars would have the same surface temperatures? Explain why. [2 marks] (c) Which star is larger, Star 2 or Star 3? And by what factor? (you do not have to show working) [2 marks]
(a) Star 1 and Star 2 have the same luminosities and therefore would also have the same absolute magnitudes. (b) Stars 1 and 5, and Stars 2 & 3. For both of these pairs, the spectral types, which indicate surface temperature, are the same. (c) Star 2 is larger by a factor of 1000 in radius.
(a) Which star has the highest luminosity (intrinsic brightness)? (b) Which star appears the brightest from Earth? (c) Which star appears faintest from Earth? (d) Which star is closest to Earth?
(a) Star C. It has the lowest absolute magnitude (-1 mag) (b) Star A. It has the lowest apparent magnitude (-1.5 mag) (c) Star B. It has the highest apparent magnitude (3 mag) (d) Star B. It has the lowest (most negative) distance modulus. OR show its distance compared to Star A which is also closer than 10pc. Dist_B = 3.98 pc, Dist_A = 6.3 pc
What is the solar system composed of?
- 1 star (the sun) - 8 planets - 165 moons - 100 Kuiper belt objects larger than d= 300 km - 10 000s of asteroids - many comets - many meteoroids (D<100m)
long period comets
- 100 000 - 1000 000 years periods - all inclinations and both regrade and retrograde orientations - thought to originate in hypothetical ORT CLOUD (50 000 au's from the sun)
Saturn
- 2nd largest planet in the solar system - flattest planet -Sidereal orbital period: 29.4 years -Sidereal Rotation period: 10 h 12 m at the equator & 10h 40 m at the poles - Axial tilt: 27 degrees - Substantial ring system lies in equatorial plane (200 000 km diameter) - The lowest density of all the planets - No solid surface -Storms and bands like on Jupiter - Winds at Saturns equator can reach speeds of 1500 km/h - Their is a vortex at Saturn's South Pole larger than earth! - Strong magnetic field - 62 moons (150 moons with unconfirmed orbits)
Gustav Kirchhoff found that
- A luminous solid/liquid/dense gas emits light over all wavelengths: the spectrum is continuous - A low-density, hot gas emits light at specific wavelengths related to the specific element: The spectrum consists of emission lines - A low density, cool gas absorbs light at specific wavelengths from a continuous spectrum. These wavelengths are related to the specific element: The spectrum consists of absorption lines superimposed on a continuous spectrum
Looking for Stellar Dark Matter
- A massive foreground objects wraps space-time and causes light to follow a curved path towards the observer - The background object appears brighter when the massive objects is in front of it - The background object dims when the massive objects move out of the lines of sight
Galaxy evolution: Galaxies interact with other galaxies
- Can cause sudden intense bursts of star formation when gas is compressed in interactions: Starburst galaxies - Can divert matter into a central black hole of one galaxy: AGN
Dark Nebulae
- Cloud lies in front of background stars and obscures them- forms dark patch on sky
Caroline Herschel (1750-1848)
- Discovered many comets - One of the first 2 women to be granted membership of the royal astronomical society. - The crater C. Herschel on the moon is named after her
Earth's Moon
- Earth's only natural satellite -Sidereal rotation period: 27.3 days -Orbit inclined at 5.2 degrees to ecliptic - Axial tilt: 6.7 degrees - Elongated in shape due to Earth's tidal forces - Heavy crater surface - No atmosphere - no magnetic field
Active Galaxy Energy Production
- Energy derived from inflating gas and stars into the central black hole in the nucleus of a galaxy. - Infalling gages forms accretion disk and through friction, heats up and emits radiation - Fuel=stars, interstellar gas (like due to interactions with another galaxy - 10-20% of inflating mass may be converted to energy before crossing black hole event horizon - Jets of material (electrons & Protons) blasted out parallel to accretion axis by strong magnetic fields - Instabilities in accretion disk can cause variability emission
Callisto (Jupiter)
- Icy and cratered - thin atmosphere - Although similar size to mercury, much less dense so must contain less rocky & metallic materials and more ice - might has a subsurface ocean - no plate tectonics no magnetic field
Callisto's Surface ( a Jupiter moon)
- Icy and heavily cratered - Valhalla basin shows ripple structure likely due to large impact: Ice has melted and resolidified before ripples dissipated
Metamorphic Rocks
- Ingenious or sedimentary rocks which are physically or chemically transformed as a result of high temperature or pressure. - Conditions when plates collide or subduction zones
The fate of the universe (1)
- It can continue to expand forever - The expansion will eventually stop and reverse into a contraction The denser it is the more likely it will be to crunch (contract) - The critical density (which is just enough to allow gravity to stop the expansion is - 9x10^-27 kg/m^3 (for H0=70 km/s/mpc) -2 H atoms per M63 omega zero (critical perimeter)
Newton's 3 Laws & Gravition
- LAW OF INERTIA: Every body continues in a state of rest or in a state of uniform motion in a straight lines, unless it is compelled to change the state by a force acting on it - When a force F acts on a body of mass M, it produces in it an acceleration A equal to the force divided by the mass F=ma - To every action there is an equal and opposite reaction - UNIVERSAL LAW OF GRAVITATION
Europa's Surface ( A Jupiter moon)
- Lack of severe cratering implies that the surface is relatively young (volcanism ect.) - This may be due to liquid water 'erupting' through cracks in the icy surface and smoothing the terrain when it freezes (not confirmed) - Processes must be ongoing with lack of obvious cratering
Ganymede (Jupiter)
- Larger than Mercury and covered in craters - Darker regions are older - Cover in ice or snow and has ice through interior - Evidence for possible plate tectonics - Small magnetic field - Likely heated inside by tidal heating by Jupiter
short period comets
- Less than 200 year periods - Tend to have orbits in roughly the ecliptic plane - Originate in the Kui[er Belt ( 30-50 Au's from the sun)
Lo Moon on Jupiter
- Lo is the most geologically active object in the solar system - > 100 active volcanoes - Orange due to Sulphur compounds in the volcanic material - Activity due to the strong tidal forces exerted by Jupiter on Lo - Very thin atmosphere consisting mainly of SÓ
The Hubble sequence/ Tuning Fork Diagram
- Map the similarities and differences between galaxies (irregular galaxies don't fit on the fork) - The evolutionary path in the diagram is WRONG -
dust
- More complex clumps of atoms and molecules (like chalk dust, smoke, soot) - Causes obscuration of star light behind it
Lo's Surface (a Jupiter Moon)
- No visible cratering - Has the youngest surface of any object in the solar system
Volcanoes on Triton (Neptune's Moon)
- Not all volcanoes are hot, some shoot out liquid nitrogen
Equatorial Mount
- One axis is aligned with Earth's Rotation acid (n to s) - Only have to move in one direction to track objects
Venus surface
- Only larger diameter craters found since smaller meteoroids will not make it to the surface through the thick atmosphere - approximately 10 x fewer larger craters on Venus then Moon/ Mercury so much of Venus's surface is young due to lava flows
Asteroids
- Orbit in a 'belt' between mars and Jupiter's orbit - Primal rock which never managed to form a planet Typed of Asteroids - C type - S type - M type & other
Reflector telescope, mirror names
- Primary Mirror: The light collecting mirror - Prime Focus: is its focus
Hierarchical Merging
- Seeds of galaxy formulation were small density fluctuations in the primordial matter of the universe - These small blobs of gas formed star clusters and then merged and merged again to become larger galaxies =++ Backed up by computer simulations and observations - Distant galaxy observations show they they were smaller and more irregular than galaxies close by
List two types of active galaxies:
- Seyfert Galaxies (they are spiral galaxies with bright, point like nuclei which vary in brightness) - Quasars (resemble Seyfert galaxies with very luminous nuclei. 10% are strong radio sources thought to be powered by jets of material moving at speeds close to the speed of light - Radio galaxies (They are distinguished by having giant radio lobes fed by one or two jets. They have a compact nucleus. and its emission lines maybe broad or narrow)
Uranus's Magnetic Field
- Strong magnetic field with axis off-set from rotation axis - A slush of ammonia dissolved in water could act as a conductor. This could be displaced from being close to the center of the planet and might lead to the weird offset in the magnetic field - Uranus is not massive enough to form the sort of pressure required to form metallic hydrogen
Europa (Jupiter)
- Surface of frozen water ice with lines crossing it. - Very few craters - surface is constantly renewing itself - water can flow and cover over impact craters - Underneath is an ocean of liquid water - very tenuous atmosphere of Oxygen
Triton's Surface (a Neptune moon)
- Surface temp: 37 K & thought to mainly consist of water ice - Lack of cratering likely due to liquid water erupting from under surface and refreezing over craters - Frozen 'lakes' of water ice have been found
Cratering
- The cratering on a surface can provide information on the age of the surface and the composition of the surface and underlying layers (AGE) - The formation of craters from objects (meteors, meteorites, and asteroids) hitting the surface of a planet or moon, particularly impact craters - Craters can also form due to volcanism
EM radiation
- The energy released in Fusion is in the form of gamma-rays - As the gamma ray photons travel through the sun they are absorbed and re-emitted and shift towards lower energies (sun's blackbody peak T-5800 K) - Therefore photons which eventually escape are not the same ones that were initially produced
Spiral density waves
- The strs and gas rotate faster then the spiral density waves - the spiral pattern is not tied to the matter in the disk - just a pattern - young stars are bluer- why spiral arms appear bluer - Star formation itself might drive the waves
eclipsing binary stars
- Two close stars that appear to be a single star varying in brightness - The variation in brightness is due to one star moving in front or behind the other star (similar to Transit method)
How do we measure the distances to galaxies?
- We can use Cepheid variable stars to measure distances to ~ 25 mpc -
What causes the two types of super nova?
- When a nova occurs, the white dwarf ejects the accreted matter off its surface - With recurrent nova, not all the material is burned or ejected each time and so the white dwarf gradually increases in mass over time
Heat Death/ Big Crunch (2)- Fate of the universe
-- If the expansion stops, then gravity will win and the Universe will star to contract -- Nearby galaxies will appear blue shifted -- density and temperature of universe will rise -- galaxies and stars will collide as space shrinks -- Universe approaches a hot, superdense singularity -- Laws of physics as we know them break down here!
Cool Death (1)- Fate of the universe
--Gravity is too weak to stop the expansion which contuse forever -- galaxies become increasingly distant from each other and fainter -- Eventually only the local group galaxies will be visible form the Milky Way -- Eventually the Milky Way will run out of fuel and no new star formation will be able to occur, temperature will decrease
If you are at latitude 30 deg south on earth, what would be the declination of a star which is directly overhead?
-30 degrees Latitude and declination are linked together
(b) Explain what causes active galaxies to appear 'active' and why the Milky Way is not an active galaxy? [3]
-Active galaxies have a supermassive black hole at their centre which is actively accreting and consuming material in an accretion disk around it resulting in non-stellar emission. [2] -The Milky Way is not active because there is nothing currently falling into the black hole at the Galactic centre. [1]
List and explain two possible candidates for dark matter
-An axion is an extremely low mass particle within the Standard Model, lighter than a neutrino - Neutrinos are a type of elementary particle that exist all across the universe and don't interact with much with other particles as they travel through space or through matter. They also have no charge.
Mars
-Axial tilt: 24 degrees -Siderreal Rotation period: 24.6 hours - Thin atmosphere: Mainly Có & N2 - Red surface color due to high levels of Fe (rust) - Cold surface, Temperature: 210k - Surface: Polar caps of CÓ & Frozen Water - Huge volcanoes (valley Marineris) - Craters - No plate tectonics no magnetic field - 2 small moons (Deimos & Phobos)
Stage 5: Protostellar Evolution
-By this stage the protostar has shrunk to 10x the size of the Sun currently, its surface temperature has increased a bit (4000 K), and it is still 10xbrighter than the Sun is today. The core temperature is hotter than the photosphere surface temperature (5 million K), but not yet hot enough for nuclear fusion to switch on. -At this stage the formation of the star proceeds more slowly. -We call the part of the evolutionary track between (4) and (6), the Hyashi track (after the astronomer who characterised it). Stars at this stage of their formation have strong stellar winds (remember the T Tauri phase in the formation of the Solar System?)
3 spectral types
-Continuous Spectra - Emission line spectra -Absorption line spectra
Gas
-Mainly individual atoms and small molecules - Very little blocking/obscuration or starlight
Triton (Neptune's moon)
-Neptunes Largest Moon, moves in retrograde -Tenuous atmosphere (mainly n2) - Surface activity in the form of nitrogen geysers which shoot nitrogen gas high into the atmosphere from below the surface - Many frozen water lakes - surface temperatures of 37 k (very cold ) - Tidal forces from Neptune dragging it closer - may be broken up into a ring system in 100 million years or so
Mars surface
-North Hemisphere is mainly huge volcanic planes - South Hemisphere is heavily cratered highlands
Jupiter
-The biggest planet in the solar system - 2x mass of all other planets combined - Axial Tilt 3 degrees to ecliptic - Sidereal rotation time (fastest) : 9h 55mins at the poles & 9h 50 mins at the equator -causes a bulge around the equator - Atmosphere: H2 & He with storm systems (Great Red Spot) - No solid surface -Strong Magnetic field - Ring System (rock and dust) - 69 moons (the 4 largest are the Galilean moons)
Explain why the disk and halo of the Milky Way are classified as separate parts of the Galaxy by describing the differences between their overall shapes, main components, and the types (ages and compositions) and orbits of their stars.
-The halo shape: is spherical -The disk shape: is disk-shaped/flat -The main components of the halo are old stars and globular clusters - no cold gas or dust - [1] -The main components of the disk are gas, stars and dust.[1] -The types of stars found in the halo: are old, metal-poor, Population II stars[1], -The types of stars found in the disk:while in the disk we find metal-rich, young stars (Population I) -The Halo Stars Orbits: have random orientations and directions[1] around the Galactic centre, -The Disk Stars Orbits: Are all in the same plane and in the same direction
Ceres is located in the asteroid belt. It was first classified as an asteroid, but now has a classification as a minor planet. Explain why according to the IAU planet criteria.
-The object must be orbiting the Sun. -The object must be roughly spherical in shape. -The object must have cleared its orbit of other debris. -----Ceres satisfies the first two criteria above but not the third as it is located in the asteroid belt and has not cleared its orbit. Therefore it is classified as a dwarf or minor planet.
Albert Einstein (1879-1955)
-The photoelectric effect - Special Relativity - General relativity
Imagine you have been trained to use a telescope and the various instruments on it including the camera and spectrograph. Explain how you would use the telescope to search for exoplanets using the radial velocity method. Be sure to explain what data you would take with the telescope and then how you would analyse it to conclude whether or not you had found a planet.
-The radial velocity method relies on detecting the effect on the host star's radial velocity due to having an orbiting planet/s. (looking for the back and forth jiggle of the star) -Observe spectra of a star over time - take many different spectra at time intervals. (1) -From the spectra, identify spectral lines and measure their shift in wavelength from rest. Calculate the radial velocity of the star at each time (per spectrum) using the Doppler formula. (1) -Plot the radial velocity vs. time graph. (1) If you see a regular back and forth pattern (e.g. a wave pattern) in the radial velocity-time graph, this indicates that the star is jiggling due to something (likely a planet) in orbit around it. (1)
Exoplanets have been found using a variety of methods. As of May 2020, the following three methods had detected exoplanets as follows: Transit measurements: 3038 planets Gravitational microlensing: 120 planets Astrometry: 10 planets Explain some of the reasons for the differences in the numbers of detections for the methods listed above. (i.e. why have some methods resulted in many detections compared to other methods with fewer detections?)
-Transit method has the highest number of detections because the Kepler space telescope mission was dedicated to specifically and efficiently searching for planets in this way. -The photometer is also relatively easy to design to detect large planets close to their stars. Gravitational microlensing has fewer detections because although surveys have been done to try to detect this effect, it relies on the chance alignment of a planetary system in front of a background star and the probability for chance alignments is quite low. -Astrometry relies on detecting the very small apparent shifts in position of stars in images and therefore requires extremely precise imaging with very high resolution which is much more difficult to achieve than the photometry method on Kepler or the gravitational lensing signal to detect.
Mercury
-closest planet to the sun (only visible for 2 hours a night) - Heavily cratered surface - No atmosphere -Sidereal Rotation: Takes 59 earth days - Sidereal Period : 88 days (1 orbit) - Large temperature variations: 100 K at night to 700k in the day - No moons - Tectonic activity, its shrinking
1. Which star is Hotter? 2. Which Star is redder? 3. Which star is brighter?
1) B is hotter - peak frequency is higher 2) A is redder - cooler, peak frequency is lower 3) A is brighter - more area under the curve
The Stages of Forming an impact crater
1. A meteoroid approached the surface of the moon 2. When it impacts the surface, it causes an explosion which breaks the meteoroid into small pieces and hearts and melts the surface of the moon due to the large amount of energy transferred into the collision. a hole (crater) is formed where the collision took place. Material (called ejecta) is flung out at high speed from the Collin/ explosion as well 3. Some the of the ejecta flies out and lands around the edges of the crater forming an ejecta blanket 4. Secondary craters may be formed by large ejecta particles hitting the surface nearby
Phases of the moon in order
1. New Moon Rise: 6am Set: 6pm 2. Waxing Crescent Rise 9am Set: 9pm 3. First Quarter Rise: 12pm Set: 12am 4. Waxing Gibbous Rise: 3pm Set: 3am 5. Full Moon Rise: 6pm Set: 6am 6. Waning Gibbous Rise: 9pm Set: 9am 7. Third Quarter/Last quarter Rise: 12am Set: 12pm 8. Waning Crescent Rise: 3am Set: 3pm
The 7 points of the copernican revolution
1. The celestial spheres (planets) do not have just one common center. (i.e. Earth not at centre) 2. The centre of Earth is not the centre of the universe, but is instead only the centre of gravity and of the lunar orbit. 3. All the spheres (planets) revolve around the Sun. 4. The ratio of Earth's distance from the Sun to the height of the firmament (distant stars) is so much smaller than the ratio of Earth's radius to the distance to the Sun that the distance to the Sun is imperceptible compared to the height of the firmament. 5. The motions appearing in the firmament are not in its motions but those of Earth. Earth performs a daily rotation around its fixed poles, while the firmament remains immobile as the highest heaven. 6. The motions of the Sun are not its motions, but the motion of Earth. 7. What appears to us as retrograde and forward motion of the planets is not their own, but that of Earth.
The broad process Laplace suggested
1. The gas cloud contracts under gravity 2. As the cloud material spins, it flattens into a disk 3. The sun forms at the center of the disk and the planets form out of the disk material around it
How to detect planets using the Astrometry method
1.Astrometry is the science (and art!) of precision measurement of stars' locations in the sky. 2. look for a minute but regular wobble in a star's position compared to the positions of other stars. If such a periodic shift is detected, it is almost certain that the star is being orbited by an unseen companion planet.
Explain in steps how you would go about measuring the distance to a star in our galaxy using the method of spectroscopic parallax. What observations would you need to do and how would you then use them to determine the star's distance?
1.Measure a star's apparent magnitude 2.Take a spectrum of the star and classify it (spectral type and luminosity class). 3.Figure out the proper absolute magnitude for that type of star 4.Then use the magnitude equation: m-M = 5log(d) -5
Two basic types of telescopes
1.Reflecting Telescopes use a mirror to gather and collect light. 2.Refracting Telescopes use a lens to gather and collect light.
The Milky Galaxy dimensions
100 000 light years / 30 000 pc or 30 npc
Uranus's moons
15 of the moons (inner moons) lie in Uranus's skied equatorial plane and orbit almost perpendicular to the ecliptic plane - Smaller outer moons orbit in retrograde orbits which are highly inclined (most likely captured object) Highest Cliff in the Solar system on Miranda (20 km high)
Edwin Hubble
1924: Found a Cepheid Variable Stars in the great nebula in Andromeda and calculated the distance between the stars too large to be inside the Milky Way
How large is the Milky Way?
20 kpc
When the baseline is 1 au and the angle is 1 arcsec what is the distance?
206265 AU AKA 1 Parsec
Saturn's magnetic field
20x weaker than Jupiters
Sidereal Day
23 hours 56 minutes
If I make an observation of a distant galaxy with with a large telescope (9 m aperture) and it takes me 2 minutes for the exposure, for how long would I need to observe the same galaxy to make an image of the same quality with a 0.8 m telescope? Calculate the exposure time,
253.1 Pi R^2 (known info)/Pi r^2 (info we are finding) Multiply the answer by the the time it takes for the known info telescope to properly expose. Explained: 9^2/.8^2 = 81/.64 = 126.5625 X 2 mins = 253.1
How many moons does Uranus have?
27 moons Mostly named after Shakespeare's plays
Matter Era Lasted
3 billion years
Speed of light
3.00 x 10^8 m/s = 300 000 km/s
How long do these solar wind particles take to reach earth
3.5 Days (1.5 x 10 ^8 km) / 500 km = 300000 (300000 km/s)/(3600 s/) =83.33 (83.33)/ (24 h/day) =3.5 DAYS For the particles to get to Earth from the sun
total surface area
4 Pi R^2
How long does it take for the Earth turn a degree?
4 mins
Cape Town is
48 mins behind the South African Standard Time
The Local Group
50 galaxies - The Milky Way is apart of a larger group of galaxies
Radiation Era lasted
50 thousand years
Sun's surface temperature
5800 K
How many elements have been identified in the sun?
67 elements and 90% of all the atoms in the sun are Hydrogen atoms
Prestellar evolution of a solar-type star
7 Stages the star like out sun goes through
The ptolemaic Model - Claudius Ptolemaeus
80 circles - probably the most complete geometric model of all times
The Sun contains how much of solar system material?
99.9% of all solar system material!
How do we define Life?
=React to their environment and heal = Grow by taking in nourishment and converting it to energy = Reproduce & pass on characteristics to offspring = Evolve to changing environments over generations
What is a galaxy?
A galaxy is a huge collection os stellar and interstellar matter (stars, gas, dust, neutron stars, black holes) isolated in space and held together by its own gravity
Light Curve
A graph of brightness versus time commonly used in analyzing variable stars and eclipsing binaries.
Hertsprung-Russell diagram (H-R diagram)
A graph that plots luminosity v. temperature of stars. The y-axis displays increasing luminosity and the x-axis displays decreasing temperature. REMEMBER they go from Hot to cold on the X axis
Galaxy Cluster
A gravitationally bound collection of galaxies
How is a black hole formed?
A mass above ~3Msun, the star will start to collapse on itself and the pull is so great that not even light can escape
Temperature
A measure of the microscopic motion/ kinetic energy from the particles making the body
Meteor(n) Shooting star(Synonym) Meteoric(adj)
A meteor event is caused by friction in the atmosphere between the air molecules and an asteroid or meteoroid which is moving thought it - Friction excites air molecules when then drop back to their ground state and emit light as the rock passes through the atmosphere
Neutrino
A particle that does not have a charge. they only interact with the weak force - Some energy carried away by neutrinos escaping the sun's core
H-R diagram (Hertzsprung-Russell diagram)
A plot of intrinsic brightness versus surface temperature for stars. When so plotted, stars' positions take the form of a main sequence for average stars, with exotic stars above or below the main sequence.
millisecond pulsar
A pulsar whose period indicates that the neutron star is rotating nearly 1000 times each second. The most likely explanation for these rapid rotators is that the neutron star has been spun up by drawing in matter from a companion star. -- Many are found in globular clusters, which is weird because Globular cluster are really old and any neutron star formed should have spun down by that time
Pulsars
A rapidly spinning neutron star that produces radio waves Person who discovered it Dame Jocelyn Bell, professor won the noble peace prize with her discovery
Hyashi Track
A representation of the changes in color and brightness of an evolving protostar.
Precession
A slow motion of Earth's axis that traces out a cone over a period of 26,000 years - Its the wobble that is due to gravitational pull of the moon and sun on earth ++ It causes a difference between the topical and sidereal year
active optics
A technique using computer-controlled mirrors to sharpen images distorted by the atmosphere
Jupiter's Great Red Spot
A storm twice as wide as Earth and has existed for at least 3 Centuries
adaptive optics
A technique in which telescope mirrors flex rapidly to compensate for the bending of starlight caused by atmospheric turbulence.
Giants are
Giants are stars with 10 Sun <R< 100Rsun
How do Nova's occur
A white dwarf in a semi- detached Binary Star System can become a nova: • If the binary companion exceeds its Roche lobe, material can spiral onto an accretion disk around the white dwarf and then spiral down onto its surface • Inner part of disk very hot due to friction within the gas and radiates in visible, UV and X-ray • Gas on surface gets denser and hotter until at 107 K, H-burning turns on! • H fuses to He very briefly, star hugely increases in brightness, then fades and blows off outer layers
Habitable Zones
AKA Goldilock zones, not too hot, not too cold
Making the outer planets: Core- accretion theory
Abundant icy grains in colder region formed more massive proto-planets faster and gravitational fields attracted large amounts of gas directly from the solar nebula.
Solar Activity: Prominences
Active regions of the photosphere close to sunspots where gas and particles erupt from the surface - They are loops/sheets of gas ejected from active regions into atmosphere (corona) (last for days/weeks or hours)
Refracting Telescope: Advantages & Disadvantages
Advantages: 1. Easy to use and consistent due to the simplicity of design. 2. Good for distant terrestrial viewing 3.Excellent for lunar, planetary and binary stargazing especially with larger apertures 4. Sealed tube protects optics and reduces image degrading air currents 5.Rugged, need little or no maintenance Disadvantages: 1.Generally have small apertures, typically 3 to 5 inches 2.Less suited for viewing small and faint deep sky objects such as distant galaxies and nebulae 3.Heavier, longer and bulkier than equivalent aperture reflectors and catadioptrics 4.Limited practical usefulness 5.Good-quality refractors cost more per inch of aperture than any other kind of telescope. Easy to use and consistent due to the simplicity of design. Good for distant terrestrial viewing
The Reflecting Telescope: Advantages & Disadvantages
Advantages: 1.Easy to use and construct 2.Excellent for faint deep sky objects such as remote galaxies, nebulae and star clusters because of their larger apertures for light gathering. 3.Low in optical irregularities and deliver very bright images Reasonably compact and portable 4.A reflector costs the least per inch of aperture compared to refractors and catadioptrics since mirrors can be produced at less cost than lenses Disadvantages: 1.Generally, not suited for terrestrial applications 2.Slight light loss due to secondary obstruction when compared with refractors 3.The tube is open to the air, which means dust on the optics even if the tube is kept under wraps 4.Reflectors may require a little more care and maintenance
Radio telescope advantages & Disadvantages
Advantages: = 24 house observing possible = weather not a big issue (clouds are not a problem) = Dust in space less of a problem = Some objects in space only emit strongly in the radio part of the spectrum Disadvantages: =Poor angular resolution = Long observing times
Care Accretion model
After a period of time, the young sun would have gone through a very active phase with strong stellar winds (called T-Tauri phase) which would have blown the lighter nebula/disk material away and stopped the future growth of the outer planets are that time.
The Kepler Mission ( march 2009 - October 2018)
Aim was to find other habitable planets in the galaxy using the transit method - found 4707 candidate planets - Kepler had a very sensitive photometer which could measure the very small change in brightness of a star if a planet passes in front of it. - 2652 confirmed planets - Planet around binary star system ( two suns) -90 system is similar to our solar system with 8 planets
Partial Eclipse
Alignment but in in Penumbra
What was the observational evidence that led astronomers to discover that the universe is expanding?
All distant galaxies are moving away from Earth and the further away they are, the faster they appear to be moving away.
blackbody curve
All objects have radiation curves with the same general shape. -Black Body is an idealized object which absorbs all radiation falling on it. In a steady state, Black body must re-emit the same energy it absorbs
The nearest star to the sun
Alpha Centauri , 4.4 Light years away
Spectroscope
An instrument that separates light into a spectrum.
end of high mass star
An iron core required energy to be put in to fuse SO KABOOMB The core collapses into a super nova
What is a standard candle?
An object in the sky whose luminosity can be precisely estimated - If we measure an object's apparent brightness and we know its intrinsic brightness, then we can measure its distance
The Doppler Effect
An observed change in the frequency of a wave when the source or observer is moving - The Doppler effect is due to the relative RADIAL velocity difference
Azimuth
Angle Clockwise from North
altitude
Angular Distance above the Hrizontal (Horizon)
Radiation
Anyway in which energy is transmitted between 2 physically. unconnected points
dark dust clouds
Are cold and very sense compared to surroundings, many parsecs across Mainly composed of Gas and some Dust
Molecules
Are groups of atoms connected with chemical bonds
Nodes
Are the two points where the moon's orbit crosses the plane of the ecliptic - In order for an eclipse to occur the moon but be at a node
Formation of Stars like the Sun (1)
As a gas cloud collapses and a star forms, both the central and surface temperatures increase
Evolutionary track of a star
As a star forms and evolves over time, it will move to different locations (in L and T) on the H-R diagram. We can join these dots into a path which is then called an evolutionary track of a star.
Formation of Stars like the Sun (2)
As the gas cloud collapses and the star forms, the diameter of the gas decreases (it shrinks). Since the mass can't change, but the diameter is shrinking (and therefore the volume as well), the density must go up
What causes the spiral arms?
As the stars, gas & dust orbit, they move through spiral density waves (waves of gas compression) which compress the gas and trigger star formation. The spiral arms cannot be caused by the differential rotation of the stars and gas in the Galaxy because eventually the spiral spiral arms would be washed out.
Matter Era
As the universe expanded and cooled, matter became dominant; atoms could survive as radiation was no longer breaking them apart Atomic Epoch ~100 million years - Atoms remained intact in the lower density radiation field - First stars formed Galactic Epoch ~ 3 Billion years - Galaxy construction Stellar Epoch ~ Current day - Galaxy evolution, continuous star formation
The image shows the measured rotation curve for the Milky Way. Explain: - why this curve was surprising to astronomers when it was first measured (what had they expected it to look like?) - what it is thought to be the reason is for the curve to look this way - and what is thought to be responsible.
Astronomers expected the rotation speed to start reducing just after the edge of the visible matter (radius ~15-20 kpc). [1]There must be more matter/mass than we can see located at higher radii from the centre which is causing the rotation velocity of the Galaxy to stay at a high speed. [1]It is thought that this mass is in the form of dark matter.
How astronomers use radial Velocity
Astronomers plot the radial velocity of the star over time to look for any changes - To make one measurement - they need to take a spectrum of the star, measure the shifts, of the spectral lines from rest position, and use the doppler formula to calc the star's radial velocity
stellar parallax
Astronomers use it to measure the distances to stars - the apparent shift in the position of a nearby star (relative to distant objects) that occurs as we view the star from different positions in Earth's orbit of the Sun each year The base line is 1 AU (Distance from the sun to the Earth)
Formation of Matter, Temperature
At high temperatures (early times) the matter and radiation were in thermal equilibrium (particles were forming and annihilating regularly) - By the time the temperate dropped to 1 billion K there wasn't enough energy for electron/position pair production. - There was more matter than ant-matter lefter over after all of the annihilations -00-- The left over protons, neutrons, and electrons froze out of the radiation field
The Start: Sun Spot Cycle
At the poles of the Sun
Seasons on Uranus
At the poles there is total darkness during summer/winter - At the Equator it is cold during summer and winter and hot in spring and autumn.
EM Radiation: Gamma-ray
Atmosphere is opaque Applications: Neuron stars, AGN
EM Radiation: Visible light applications
Atmosphere is transparent, can see straight through shit Applications: Planets, stars & stellar evolution, normal & active galaxies, large scale structure
EM Radiation: X-ray applications
Atmosphere opaque- space based observations - need special mirror design Applications: Stellar atmospheres, neutron stars, & blackholes, AGN, hot gas in galaxy clusters
Isotopes
Atoms of the same element that have different numbers of neutrons
Earth
Axial tile: 23.5 Sideral Day: 23h 56m Atmosphere: N2 (78%), Ó (21%), Ar (.9%), CÓ(0.03%) - Greenhouse effect causes warm temperatures on surface
Mars's Surface : Olympus Mons
Biggest Volcano in solar system - 700 km across base and 25 km high at peak! (3 times higher than Mount. Everest
Method: Gravitation Microlensing
Based on 'by change alignments of a star with an orbiting planet happening to move in front of a more distant start from the point of view of the observer
Why do some planets/moons have more/less craters than others?
Because if a planet/moon is more geologically active with volcanism and more when a crater hits the surface it impact will be virtually removed through things eroding and or cover the mess - Also Atmospheres, thick atmospheres stop smaller meteoroids from getting to the surface
Galaxies and Dark Matter in our galaxy
Because the rotation curve of our galaxy didn't drop off as we got to the edge of the observable galaxy. The velocities were flat even at high radi which means that there must be extra matter that is attributed to it
Our current model of Dark Matter is that is has always
Been the same
Does structure ever hit maximum size in the universe
Both all sky shallow and deep pencil beam surveys agree that there does not seem to be more structures larger than 200-300 mpc in size - thats like the MAX
Jupiter's belts and zones
Bright/ light zones and dark belts from convection in the atmosphere The reason for the belts and zones is Jupiter's fast rotation. This speaks high and low pressure systems around the planet unlike on Earth where they are localized circulating storms
Failed star is known as a ?
Brown Dwarf
Tycho Brahe (1546-1601)
Built observatory "Urabiborg" and observed by eye - stars - planets - supernova -comet Geo-heliocentric system: The sun and moon orbit Earth, and everything else orbits the sun
bulge
Bulge: Like a rugby ball which might meant that the milky is a barred spiral galaxy (redder than disk. The inner region there is dust, gas, stars. you find both old and new stars (star formation) The outer region- not much gas & stars similar to halo. they are also redder
White dwarf mass limit
Chandrasekhar Limit = 1.4 Msun
How long has it taken any galaxy to get to its current distance form us?
Calculate time : Distance/velocity Velocity =H0xdistance Ho=70km/s/MPC 1/H0 =14 Billion Implications: - Everything in the universe (matter and radiation) was confined to a single point 14 billion years ago (the primeval fireball) - The universe then expanded very fast: The Big Bang - The age of the universe is ~14 billion years (just need the Hubble constant) - The age of the universe is finite
Mercury's surface
Caloris Basin - Very large impact (crater estimated at 550 km across) Weird Terrain on the opposite side, it is thought that seismic waves, caused by the large impact, refocused on the opposite side of the planet and caused strange surface disruptions there
linear momentum
Can be thought of as the tendency of an object to keep moving in a straight line. p=mv Product of Mass X Velocity
angular momentum
Can be thought of as the tendency of an object to keep rotating or spinning L ∝mass x rotation rate x r2 (radius squared)
Hubble's laws application
Can be used to find the distance to very distant objects
Utilizing the Transit Method
Can only confirm a planet if we see at least 2 dips in the host star's light curve (whole orbital period and then some) - We don't have enough time yet to confirm longer period orbits - Will make the incorrect conclusion that there are only planets with short orbital periods
Sagittarius A Star
Candidate for the central black hole at the Galactic centre id the object - Radio X Ray, Gamma ray observations indicate energy output ~10^33 W (Million times the sun's output)
The time on your watch says 1:30pm, what is the local solar time in Cape Town?
Cape Town is behind SAST, so the local solar time would be 12:42pm
Jupiter's magnetic field
Causes dynamo effect generating powerful field producing rings of auroras around planet's magnetic poles, interacts with small moon Io and traps high-energy particles to form intense radiation belts. - Liquid Metallic H inside Jupiter + Rapid rotation likely causes the strong magnetic field (DYNAMO Effect) - 20 000 times stronger than Earth's
Life on earth is ____ based
carbon based
How did life start?
Chemicals on the young earth and its primitive atmosphere may have been processed by lightning, volcanic activity, Uv radiation, natural radioactivity into amino acids (building blacks for portends which are vital for life.
Luminosity Class
Classify stars according to width of spectral lines Spectral Type (OBAFGKM) Luminosity Class = Bright Super Giant Ia, Super Giant Ib, Bright Giants II, Giants III, SubgiantsIV, Main sequence stars and dwarfs V
The End: Sun Spot Cycle
Close to Equator
Who found Pluto?
Clyde Tombaugh in 1930 , 5 moons
Comets
Comest travel in a highly elliptical orbit around the sun at one focus - as they approach the sun they get right and they melt a develop. tail (does not emit its own light) - Nuleus on only a few KM in dimmest
Radial Motion
Component away/towards the sun How to Measure - Take A spectrum of the star and look for a shift in spectrum lines and then compare them at their rest wavelengths. If there is a shift to shorter wavelengths the star is moving towards you and if it shifting to longer wavelengths then it is moving away (red shift) Measure using Doppler Shifts, Kilometers per second
M type + other asteroids
Contain large fractions of nickel & iron (metals) - 10% of all asteroids
Moon's surface
Crater counting on other planets can be compared to Moon crater counts to get relative ages of surfaces
The Moon's Surface
Cratering due to meteoroids which impact the surface since there is no atmosphere. - (Cratering) Highlands & (no craters) Darker parts as Maria
Lava domes are
Created from upwelling lava which then recedes and the surface cools & solidifies
What would be the parallax of a star which is 10 pc from the sun?
Distance (PC) =1/Parallax 10 pc = 1/parallax 1/10 = 0.1 Arc Seconds
Q3. Which of the following stars is closest to us? A. Procyon (parallax angle = 0.29 arcsec) B. Ross 780 (parallax angle = 0.21 arcsec) C. Regulus (parallax angle = 0.04 arcsec) D. Sirius (parallax angle = 0.38 arcsec)
D. Sirius
To find distance, knowing apparent & absolute magnitudes
D=10pcx10^-(M-m)/5
The thing causing the universe to exand
Dark Energy - a force that works opposite to gravity - The bigger the universe gets, the more Dark Energy dominates over gravity
Dark Matter Halos of Galaxies
Dark Matter halos surrounding galaxies make them much larger than their optical sixes indicate and more likely to interact o emerge *since they are closer together than they look!)
Latitude (N or S)
Declination (deg, armin, arc seconds)
Units
Declination: 1 degree= 60' (arcmin)=3600'' (arcsec) Right Ascension= 1 hour = 60 min = 3600 s (1 hour =360 degrees/24 hours = 15 degrees)
Venus has
Dense clouds or sulphuric acid - Surface temperature is 730 K from runaway greenhouse gas effect - No moons
Type of Merger (2) Spiral arms possible formation
Depending on the masses and sizes of interacting galaxies, different results will occur Size of Galaxy A< Size of Galaxy B but M Galaxy A~ M Galaxy B - Distortion of galaxy shapes - Possible formation of spiral arms Similar sized galaxies collide
Formation of the Solar System: Nebular Theory
Descartes (1600s) and Laplace (1700s) suggested that the planets were formed as part of the sun's formation. - A large nebula of gas contracts under its own gravity, becoming denser and hotter until eventually it forms a star (the sun) at its centre. - Planets and moons form in the cooler outer regions Laplace showed that the nebula must spin faster when contracting (conservation of angular momentum): - Causes flattening of the system (like a pancake) - SOLAR NEBULA PLANETS FORMED FROM THE SPINNING MATERIAL
Types of Binary Stars
Detached Binary: Both stars lie inside their Roche lobes and do not interfere with each other Semi-Detached/Mass-transfer Binary: If a star evolves and its size overflows its Roche lobe, gas can flow onto the other star Contact Binary: If both stars overflow their Roche Lobes, their surfaces will merge and the system will have two cores surrounded by a single envelope
Islamic Astronomy
Developed Trigonometry (zenith, Azimuth), developed measurement instruments - Star names - Betelgeuse, Rigel, Vega ++ Developed trigonometry methods (needed to find direction to Mecca)
Active Galaxies / Active Galactic Nuclei Spectra
Different Spectra from normal galaxies Radiation from Active Galaxies is NON STELLAR - Not from stars -
Tidal forces are differential forces
Differential Forces- The gravitation force from the Moon on the Earth is not constant across the Earth's diameter- The close die is more strongly pulled than the furthest side.
Differentiation
Differentiated means that the inner and outer planets are composed of rather different constituents and have different structures - There are variations in the density and composition of a planet/moon with distance from its center
How do we measure the sizes of stars?
Directly (Speckle Interferometry) or Indirectly (Luminosity)
Size of Stars : Two ways
Directly or Indirectly
William Herschel
Discovered Uranus
Uranus
Discovered by William Herschel - Sidereal Rotation: 14.2 H at poles & 17.2 h at the equator - Sidereal Orbital Period : 83.75 years - Axial Tilt is 98 degrees (tipped on its side) - Atmosphere: H2, He, methane (colour due to methane) - Some weather and clouds but very low in the atmosphere so hard to see - strong magnetic field with axis off set from rotation axis FASTER AT POLES & SLOWER AT EQUATOR - Has rings (thin and widely spaced) - 27 moons (5 medium sized)
Sir William Herschel (1738 -1822)
Discovered many double stars & nebulae - Discovered Uranus! - Mapped Distribution of stars and nebulae and suggested some spiral nebulae might be distant systems like our own - Infra-red radiation
3 main components of the Milk Way
Disk: Younger stars closer to the disk and older stars have drifted away. A lot of gas and dust, there is active star formation. They dominate the color of the disk (blue) - Stars in Halo is Metal rich (population II) Bulge: Like a rugby ball which might meant that the milky is a barred spiral galaxy (redder than disk. The inner region there is dust, gas, stars. you find both old and new stars (star formation) The outer region- not much gas & stars similar to halo. they are also redder Halo: Is thought to be older than the disk and bulge parts (almost no gas or dust, stars are more redder than disk stars living in globular clusters (super old) no ongoing star formation. - Stars in Halo are metal poor (heavier than Helium) because the interstellar medium didn't have metal yet (Population 1)
Using Parallax to Fine Distance
Distance (PC) =1/Parallax - 1 parsec = 1 per arcsec - 1pc ~ 206265 AU = 1pc =3.3 light Years
How many Parsecs would a star be from the sun if its parallax = 0.5 ?
Distance (PC) =1/Parallax 1/0.5 = 2
If a light source is approaching you, you will observe
Its spectral lines are shorter in wavelength- Blueshift
An advantage of CCDs over photographic film is a) they don't require chemical development. b) digital data is easily stored & transmitted. c) CCDs are more light sensitive than film. d) CCD images can be developed faster. e) All of the above are true.
E- All of the above are true
To jump up from ground state to excited state
E- has to absorb energy equal to energy level gap -Absorption of a photon: E- in ground state absorbs photon and jumps up to first excited state First excited state: N=2
To jump down from excited state to lower energy level
E- has to loose energy equal to energy level gap Emission of a photon: E- in first excited state emits a photon and drops down to ground state Ground state: N=1
How much energy would the sun cause to be radiated if it fell into the black hole?
E=mc^2
Earth is closer to the Sun in January. From this fact, Kepler's 2nd law tells us
Earth orbits faster in January - Kepler's 2nd law means that a planet moves father when closer to the star
Earth's surface
Earth's atmosphere protects it form smaller meteoroids as they burn upon entry, but some still make it through. - Barringer Crater, Winslow Arizona (25 000 years old)
What causes Earth's seasons?
Earth's rotational axis is tilted 23.5 degrees
Predicting eclipses
Eclipses recur with the 18-year, 11 1/3-day saros cycle, but type (e.g., partial, total) and location may vary.
Galaxy Classification Scheme
Edwin Hubble in 1924 was the first person to make a comprehensive galaxy classification scheme --- - Spirals -Barred Spirals - Ellipticals - Lenticulars (meaning lens-shaped) - Irregulars
Galaxies come in all shapes and sizes. List the five main galaxy types on the Hubble sequence and also give their abbreviations.
Elliptical - E Lenticular - S0 or SB0 Spiral - S Barred Spiral - SB Irregular - Irr
Upon which property of the moon's orbit around the earth does the type of solar eclipse depend?
Elliptical orbit - distance from earth varies over the month
Emission nebulae radiate mainly in the ultraviolet part of the electromagnetic spectrum.
Emission nebulae are glowing clouds of hot interstellar matter. The 'M' stands for Messier after Charles Messier who made a catalog in the 1700s of fuzzy objects in the sky not be confused with comets (so that people could recognise new comets and didn't mix them up!).
Radio Galaxies
Emit large amounts of energy at radio wavelengths and have different emitting regions to Seyfets (elliptical galaxy) - Weirdly it has dust though elliptical galaxies don't have dust. E2 galaxy might have formed through collision with a spiral - Jets of material ejected from the nucleus outer lobes must be few 100 million years old Properties: - Usually have huge radio lobes (clouds of gas) displaced from nucleus along jets. which emit energy and extend past visible galaxy - radio lobes alone emit 10x more energy than Milky Way at ALL wavelengths
Stage 3: Fragmentation Stops
Ends when we can see a photosphere on the protostar... • Fragment size ~ solar system (continuing to shrink) • core density high enough for radiation to be trapped (1018 particles/m3) - core starts to heat up (10 000 K) • outer temperature still cool (~100 K)• dense, opaque central region = PROTOSTAR• end of stage 3: protostar has a photosphere protostar mass increases as material rains down on it, but size continues to decrease since gravity is still beating heat
2 Solar Structure: Radiation Zone
Energy transported by radiation
James Clerk Maxwell
Explained Saturn's rings
Dust Affects starlight in 2 ways
Extinction: Overall Dimming of starlight by ISM , Side of dust grains determine which wavelengths of light affected (affects short wavelengths more) Redding: Star appears redder since shorter wavelengths (blue light) are absorbed/scatter more easily
All active galaxies are observed to have large radio lobes extending from their nuclei.True / False [1]
F
F ring (Saturn)
F - Ring has a kink in its structure due to interaction of shepherd moons (prometheus & Pandora) which 'steer' the ring particles in a particular direction due to their gravitational tugs
Determining Exoplanet properties: Planet Mass
F= G (Mm/a^2) A^2- semi major axis
Measuring a planet's mass
F= G x m1 x m2/ R^2 G= Gravitation Constant M= Mass R= Radius
What is the absolute Magnitude when I know the apparent magnitude?
Factor 10 change in distance = factor 100 in brightness (difference of 5 magnitude) Add or subtract 5 to the original number
Lenticular galaxy
Falls between elliptical & spiral. They have disks but no spiral arms, some even have bars. -Thin disk of stars BUT no gas and NO spiral arms - Flattened bulge
All massive stars end their lives as Type I supernovae.
False
Compared with Earth, Venus is much smaller.
False
Dark energy is responsible for the decelerating expansion of the universe.
False
Diffraction bends shorter wavelength light more than longer wavelength light which is why the resolution of optical images is better than the radio images for optical and radio telescopes with the same apertures.
False
Globular clusters trace out the large scale structure of the Galactic disk.
False
Interstellar matter is quite evenly distributed throughout the Milky Way Galaxy.True / False
False
Once a white dwarf star has finally cooled down to almost zero, it is called a brown dwarf.
False
Saturn is the second largest planet in our Solar System and the only one with a ring system
False
The Oort cloud is the large cloud of gas surrounding a comet while it is near the Sun
False
The density and temperature of the solar corona are much higher than in the photosphere.
False
The formation of iron in the core of a massive star leads to a Type I supernova.
False
The most abundant gas in Earth's atmosphere is oxygen.
False
The spectrum of an active galaxy is well-described by a blackbody curve.
False
Venus has a retrograde orbit around the Sun
False
Copernicus was placed under house-arrest by the Catholic church because of his heretical belief in the geocentric system.True / False
False, That was Galileo
If the moon's orbit around the Earth was larger, lunar eclipses would be more likely to be annular.
False, because Earth Is tilted on its axis and also the moon has to line up with certain nodes in order for there to be perfect alignment.
Stage 6: A Newborn Star
Finally, after the protostar has shrunk enough that the central core temperature has increased to 10 million K, it is hot enough for nuclear fusion to start! (Stage 6)We can now call the protostar a star.
Star: Direct Measurements
Fir very large stars which are close by astronomers can directly image these stars and measure their sized - Use speckle interferometry and adaptive optics to counteract-seeing problems
First Telescope history
First Telescopes were refracting telescopes designed and built by Hans Lippershey and Zacharias Janssen in 1608 as a 'spy glass' - Galileo is thought to have built the first telescope to be used for astronomy shortly after.
quasars (quasi-stellar radio sources)
First discovered through radio emission, followed up at optical wavelengths - by 1960 there were hundreds of radio sources known with no optical counterparts (faint blue star, but not a star) - The most distant thing moving fast that was highly red shifted H lines & look faint because they are sooo far BUT THEY ARE SUPER BRIGHT
Newton's 2nd Law of Motion
Force = mass x acceleration
We have a _____ Universe
Flat
Tardigrades (water bears)
Fleshy, unjointed legs Very tiny; no circulatory or gas exchange systems Some species live on water films on plants; when the water dries, they shrink and enter a dormant state that can last at least 10 years THEY ARE VERY RESILIENT
Trojan asteroids
Follow Jupiter's orbit - Lagrange Points: L1, L2,L3,L4
To calculate the highest altitude the sun would reach in the sky you would
For Winter= 90-Latitude+23.5 For Summer= 90-Latitude-23.5
Why do some planets/ moons have atmospheres and other do not?
For a given gas at. a particular temperature, the particles have a velocity distribution - some move faster, other slower and in order for particles to escape the atmosphere they have to move faster than the ESCAPE Velocity . If earth moves at 100 km then you must go 101 km to escape. All planet atmospheres slowly leak into space
Formation of the Milky way
Formed 10 billion years ago and various models exist to desire the observed data - gas clouds that caused it to collapse and the dust and gas would flatten to cause a star to be formed and over time it gets older and the stars move off the main sequence and become redder
Spicules
Found in the Chromosphere - Jets of hot matter form solar storms, might be due to disturbances in sun's magnetic field in outer layers
Stage 2: Collapsing Cloud Fragment
Fragments keep shrinking and fragmenting until the density is high enough that radiation cannot escape T rises → pressure increases →fragmentation stops • size ~ 100 x solar system • mass = 1-2 Msun • Such low density that radiation escapes and cloud fragment stays cool • Temperature:• mostly still ~ 10 K• at the centre ~ 100 K - When the Fragment has shrunk enough that the density is high enough that the photons produced can't escape anymore, then the overall temp will start to increase, the pressure, and fragmentation will start to increase
Stage 7: Main Sequence
From Stage 6 to Stage 7 takes a much longer time that it took to go from Stage 1 to Stage 6! -Eventually, the star has shrunk enough so that it reaches hydrostatic equilibrium where the outward pressure from the enormous core temperature is balanced with the inward pull of gravity. -The star is now no longer shrinking, but stays the same size during its lifetime on the Main Sequence Rate of nuclear energy generation = rate of radiation outward pressure force = inward force of gravity • core density: 105 kg/m3 (compare to water ...) • central Temp ~ 15 million K • surface Temp ~ 5800 K
Dark matter in the universe:
From galaxy and cluster measurements >90% of matter in the universe is Dark Matter and emits no EM radiation
Galaxy Collisions in Clusters
Galaxies usually form in clusters -If the speeds of the galaxies are high enough - they might pass through each other, disturbing their structures - If the speeds are low, they may "stick" together or merge
Active Galaxies (AGN)
Galaxies which have abnormal activity related to violent events occurring in/near the galactic nucleus 0 They have High Luminosity 10^10 Sun
Who discovered Sun sunspots?
Galileo
Kepler
German astronomer who first stated laws of planetary motion (1571-1630)
A CONSTELLATION is a
Group of stars which appear in the same area of the sky and seem to make a recognizable fixed pattern.
Jupiter's atmosphere
H2 (86.1%) He (13.8%) Plus smaller increments of CH4, NH3, H20
Halo
Halo: Is thought to be older than the disk and bulge parts (almost no gas or dust, stars are more redder than disk stars living in globular clusters (super old) no ongoing star formation. - Stars in Halo are metal poor (heavier than Helium) because the interstellar medium didn't have metal yet (Population 1) - Random orbits
Energy Production in the sun
Happens in the core of the sun where temperatures are high enough for nuclear fusion Mass difference = energy released E=mc^2
Great debate in 1919
Harlow Shapley thought that the Milky Way the entire universe & Heber Curtis thought the Milky Way is just one of the many galaxies (Island Universe Idea)
6 Solar Structure: Transition Zone
High Temperatures
How do Jupiter sized planets lang up so close to their parent stars??!?
Hot Jupiters, from modeling, astronomers have found it is possible for these planets as they are forming in the proto-planetary disk, to lose angular momentum to drag and move inwards towards their star.
Rigel Appears as a bright bluish star, while Betelgeuse appears as a bright reddish star. Rigel is ________ Betelgeuse.
Hotter than
Sideral Period
How long it takes a planet to make one orbit around the Sun with respect to the stars
Not involved in the outer layers of the Sun:
Hydrogen burning
IAU Planet Definition
IAU Planet Definition 1. the body orbits the Sun 2. the body is massive enough that its own gravity causes it to be roughly spherical 3. it has 'cleared the neighbourhood' around its orbit of other bodies if 2/3 are met its a dwarf planet AKA pluto
Determining Exoplanet properties: Planet radius
If a transit measurement is made, we can estimate the ratio of the planet's radius to that of its star. We can Estimate its host star's radius from its brightness and thereby get an estimate of the size of the plate Drop = r^2/ R^2 - Using this method: you make the incorrect conclusion that there are very few high mass planets more than 10 Au from their host stars, or that there are very few high mass planets very close to their stars
ring formation
If an object comes too close to a larger one it can be pulled apart F tidal > F gravity All the Major Planetary rings for all Jovian planets are within the planet's Roche limits
Galaxy Evolution
If galaxies were not interacting with each other at all, we would expect them to evolve as their stars do: Ellipticals: - Become fainter and redder over time since no gas to make new stars and once massive stars are burnt out, they are not replaced Spiral & Irregulars - Gas reservoirs allow continued star formation for longer and they will appear blue (from young stars) until finally gas runs out BUT Galaxies interact with other galaxies
Tidal Forces
If the tidal forces acting on the body are greater than its own gravitation forces holding it together, then it will be pulled apart (broken into smaller bits)
Olber's Paradox: Why is the night sky dark
If the universe were then we would expect the night sky to be as bright as the surface of the sun - An observer's line of sight would eventually end on a star in every direction - Although fluxdecreases in 1/d^2 the number of stars increases with d^2 so the sky should appear very bright - Olver was the astronomer who popularized this paradox in 1800's
Determining Exoplanet properties: Planet Density
If we know its mass and its radius, we can calculate its density. In this way we can compare to the densities of planets in our solar system and determine if the planet is a gas giant of most likely rocky. P= M/V = M/R^3
Tully-Fisher relation
If we measure a spiral galaxy's rotation velocity, we can estimate its luminosity. If we know its apparent brightness, we can then find its distance - Use 21 cm radio line from neutral hydrogen to measure rotation velocity
Meridian
Imaginary line connecting N and S and passing through the Zenith
Galileo Galilei (1564-1642)
Important Observations ‣ Surface of the moon (craters, mountains, valleys) ‣ Sunspots (showed solar rotation) ‣ Phases of Venus (orbit of Venus around the Sun) ‣ Moons of Jupiter (strongest support for heliocentric model, Earth not centre of all things)
Rilles on the moon's surface
Law flow channels
Galaxy Collisions
In the dense environments to galaxy clusters, there is a high probability that galaxies will collide
Harlow Shapley
In the early 1900's Harlow Shapley used variable stars in globular clusters to measure the 3D distribution of Globular clusters in the Galaxy. He FOUND that: - Globular clusters are found @ Huge distances from the sun (1000s of pc) - Globular clusters map out a spherical volume of space ~30 kpc in diameter - Center of distribution is nowhere near the sun (~8kpc away): Galactice centre - Sun no longer the center of the Galaxy 0 we live in the suburbs
Stars in a constellation are
In the same part of the sky
convection zone
In this layer of the sun the energy transported by physical motion of the gas is called convection.
Making the outer planets: Gravitational Instability Theory
Instabilities in the young solar nebula resulted in collapse of gas into proto-plaents directly (no condensation needed)
Kuiper belt & Trans- neptunian objects
Is located in the plane of the ecplitic about 30 - 50 Aus from the sun, outside the orbit of Neptune - Many small rocky and Icy objects orbit at this distance - Pluto - Trans- Neptunian objects (Tno's) include KBOs and all small objects orbiting the Sun beyond Neptune
What determines a star's position on the H-R Diagram?
Its how much mass it has and its composition
What does intensity mean for a particle model of light?
Intensity=number of photons! - Higher intensity (brighter color) = more photons ++++- Hence why more e- is ejected when intensity was increased during the study of the photoelectric effect
Julian Calendar
Introduced by Julius Caesar, completed by Emperor Augustus. - It corrected the drift of the calendar to the seasons. Introduced leap year giving an extra day every 4 years
Ancient Babylonians
Invented the Zodiac (to predict future of nation + skin only) 7 Gods- 7 Days of the week
Gravity vs. heat
Inward Pull of gravity vs. outward pressure due to heat (motion of particles) Mass must be extremely large ignorer to collapse to create star The picture above shows: (a) gravity pulls the particles together because they all have mass and attract each other (b)the particles come closer together (c) because the gas has a temperature (i.e. the particles all have kinetic energy), they can move apart again
Sun's Magnetic Field
Is a combination of differential rotation and convection causes the magnetic field of the sun to be twisted and change direction Different polarity orientation because the rotation is is not uniformed due to rotation and convection.
Opacity
Is a measure of how much radiation is blocked by a material (in this case the Earth Atmosphere
Parallax
Is the apparent change in position of a foreground object compared to the background due to the observer changing their position
Refraction
Is the change in direction of propagation if a wave due to a change in the medium through which the wave is moving - Refraction results in the 'Bending' of light as it passes from one medium to another (why the straw looks bent in water)
Period (P)
Is the time taken for a wave to repair itself (peak to peak)
sidereal month
Is the time the moon takes to go once around the celestial sphere... 27.3 days
cosmology
Is trying to understand how the universe came about, its history and structure and how its going to evolve in the future
The solar Cycle
Is two sun spot cycles = 22 years Every 11 years the magnetic field flips
Spiral galaxies seem to have been more common at higher redshifts. In addition they are observed to be rare in dense environments such as the centres of galaxy clusters. What is a possible explanation for what has happened to the spiral galaxies?There are several theories on Galactic mergers. But there is belief that Spiral Galaxies merged to create Elliptical galaxies long ago.
It is most likely that spiral galaxies have evolved through interactions and/or mergers with other galaxies which have destroyed their original shapes or changed them into a combined galaxy with an elliptical structure.
Possible galaxy evolution scenarios
It seems that the difference between active and normal galaxies is just a matter of fuel supply for the central supermassive black holes at their centre.
Radio Astronomy: History
It started in 1931 by Karl Jansky, researching sources of interference for short wave radio communications for bell labs - Discovered radio emission from the center of the Milky Way
Measuring the cosmic expansion
It turns out the universe is expanding at an accelerated rate.
Isotropic
Its the same in all directions. The same depth and field of view
Outer Jovian Planets
Jupiter, Saturn, Uranus, Neptune
Jupiter rings
Jupiters rings were created by meteoric impacts on small nearby moons.
Kepler's 3 Laws of Planetary Motion
Kepler 1: The orbital paths of the planets are elliptical, with the sun at one focus Kepler 2: The imaginary line joining the Sun & planet sweeps out equal area in equal time Kepler 3: The square of a planer's orbital period is proportional to the cube of its semi-major axis _ planets move faster closer to the sun & planets with a more elliptical orbit have greater changes in speed over its orbit
How can we calculate the mass of the milky way?
Kepler 3rd law Mass [Mass sun]= Orbital distance (AU^3)/Orbital Period [years]^2
Why is the night sky dark? - Solution
Key point: the AGE of the universe is finite (14 billion years) - there are things so far away that their light didn't have enough time to reach us
Venus facts
Known as 'morning star' or 'evening star' - almost the exact same size as Earth (R=6052) - No moons -Gravitational pull: 082 x m_earth - Orbit is inside Earths orbit. - Thick Atmosphere: Cox (96.5%) & N2 (3.5%) - Green house effect causes very high surface temperatures (730k) - Clouds of sulphuric acid (very reflective) - Axis tile is 177.4 degrees (whens S pole is at the top and rotates in opposite direction to the other planets - Sidereal rotation: 243 days Sidereal period: (1 orbit) is 225 days - Venus has 2 large continent like areas (high and low Lands) - No moons - No magnetic field (very slow rotation)
Measure Luminosity
L = 4πR^2σT^4
Jovian planets (gas giants)
Large, low density, gaseous/liquid Jupiter & Saturn Gaseous molecular hydrogen Liquid Metallic Hydrogen Iron- Silicate Core Uranus & Neptune Gaseous molecular hydrogen crust Liquide molecular hydrogen mantle High density slush (water, clouds with ammonia) Rocky Iron- Silicate core
Seyfert Galaxies
Lie between normal galaxies and most energetic active galaxies - Named after carl Seyfert in 1943 - Normally spiral galaxies Properties - "Normal" emission from disk and spiral arms - Most radiation is from the Nucleus: 10 000 times brighter than the center of the center of the Milky Way - Majority of light emitted is in Infrared -Variable Luminosity: Can change <1 year! There fore very compact source of energy emissions (<1 light year)
Spectral Lines: Line Broadening
Lines broaden due to environment: • thermal motions (Temperature) (hotter gas → more thermal motion → broader line) • rotational broadening• turbulence (not temperature related!) • collisional broadening (atoms colliding at same time as emitting photons) increases with density • magnetic fields (Zeeman effect) - energy levels split in presence of magnetic fields
higher mass stars
Live shorter lives, they move on horizontal tracks on H-R diagram ( unlike lower mass stars which move vertically) Luminosity stays ~ Constant and radius rises and temperature falls
The Galilean moons
Lo , Europa, Ganymede, Callisto
the moon with the densest atmosphere in the Solar System
Lo, Jupiter
5 Solar Structure:Chromosphere
Lower Atmosphere
A star identical to the sun would be where on the H-R Diagram?
Luminosity 1 and on the main sequence
Apparent Brightness Equation
Luminosity/Distance ^2
What kind of eclipse would occur if the Sun, Moon, and Earth were perfectly aligned, such that the Earth was between the Sun and the moon?
Lunar Eclipse
Would Distance be <,> or = 10 pc if the distance modulus is a negative number
M is a bigger number that means it appear dimmer at 10 pc so the star is closer than 10 pc
Compare absolute magnitude (M) using luminosity (L):
M2-M1=-2.5 log (L2/L1) M2 is what you know
Solar Activity: Coronal Mass Ejections
Magnetic bubbles of ionized gas ejected into space - If their magnetic fields merge with Earth's (called reconnection). they can disrupt communication etc.
What causes sun spots?
Magnetic field of the sun - Field lines exciting and re-entering the sun's surface and they are cooler than their surrounding because the magnetic fields block convection flow of gas towards surface in those regions
Earth's magnetic field
Magnetic lines of force from Earth's polar north and south, acting like a giant magnet. THEY SWITCH every .5 million years
William Herschel
Mapped the galaxy by counting stars in the late 1700s but not quite accurate
The Moon: Maria
Maria are 'oceans' of solidified lava and upwellings of molten material though the crust (i.g from volcanoes)
Mars surface (add)
Mars has some "splosh" craters e.g. duty crater, which implies that there is water-ice below the surface which melons on impact and gives fluid like appearance to ejecta
Using the sun's orbit, how massive is the galaxy?
Mass = 9x 10^10 M sun BUT this is the mass inside the sun's orbit We need to measure orbits of objects further out
Type of Merger:Galactic Cannibalism
Mass of Galaxy A. << Mass of Galaxy B = Galactic Cannibalism Reason why very massive galaxies seem to lie at cluster centers (ex: Spireweb Galaxy) - We think the Milky Way was a cannibal because in the Milky Way halo - streams of stars are found with similar orbits and compositions
3 Solar Structure: Convection Zone
Material in constant convection motion
Neptune
Mathematicians Leverrier and Adams predicted its orbit and Johannes Galle found it (1846) -Sidereal Rotation rate: Average 17.3 h - Axial Tilt: 29.6 degrees - Sidereal Orbital Period: 163.7 years - Atmosphere:H2, He, Methane (color due to methane) - Cloud visible in atmosphere, upper levels warmer than Uranus - Strong magnetic field with axis off-set from rotation axis - has 3 dark rings - 13 moons (1 large moon, triton) - All moons move in retrograde
Amplitude (A)
Maximum distance from undisturbed state
What methods do we use to measure distance in the universe?
Measure distance - Radar (-1AU) - Stellar parallax (-200 pc) - Spectroscopic parallax( -10,000 pc)
Transit Measurements
Measure how bright the star is and how this changes over time. _ Every time the planet orbit he star/ moves in front of it, the star goes a little dim. Intensity vs. Time = the light curve - Astronomers take this information and test it twice to confirm it is a planet.
absolute magnitude
Measures stars apparent magnitude when it is viewed at a distance of 10 pc from Sun (Symbol: M)
Mercury's orbit
Mercury's orbital e= 0.21 is tilted and the only one with this weird orbit
Inner Terrestrial Planets
Mercury, Venus, Earth, Mars
Order of the planets
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune
What is our Galaxy?
Milky Way / The Galaxy
If observe sunspots forming at 30 degrees N and S of the equator, what could I say about where the Sun is in its cycle and why?
Model Short Answer: At the start of a sunspot cycle, new sunspots form at 30 degrees N and S on the Sun. As the 11 years proceed, new sunspots form closer and closer to the solar equator. Therefore if we observe sunspots forming at 30 degrees N and S on the Sun, then it must be the beginning of a new sunspot cycle.
Discovery of Exoplanets
Most exoplanets are not found by directly imaging them, but rather by indirect methods, mainly: • radial velocity measurements (880)• transit measurements (3038)• astrometry (10) • gravitational microlensing (120)• Imaging (139)• pulsar timing (43) - Exoplanets do not emit their own light, they reflect the light from their host stars (just like our own planets. Therefore, a distant planet will appear both very small and very faint from Earth.
Volcanoes on Lo
Most geologically active object in the solar system over 80 active volcanoes - 2000 K in temperature (much hotter than earths volcanoes) - Activity due to Jupiter's tidal forces pulling on the moon flex and squeeze its interior and heats it
binary system
Most stars are part of multiple star systems, majority are binary systems
altitude-azimuth mount
Moves in two direction to track objects in the sky... Up and down and side to side
Are we at the centre of the universe
NO - Every observer in the universe sees the expansion described by Hubbles law and H0 is the same everywhere
What Significance have stars has to people through the ages?
Navigation, Mythology/Religion,
The Radiation Zone
Near the core the high temperatures means that the gas is ionized. The photons travel freely through the ionized gas without interacting with electrons in atoms (since there are only ions). The energy transported is by radiation
What could be the reasons that too few neutrinos were measured?
Neutrinos come in 3 types and cal oscillate/ change between types
What's left after a supernova?
Neutron Star - composed of Neutrons packed in a tight ball - the star is solid and is supported from collapsing by neutron degeneracy (can'y squash anymore tighter) - Very strong magnetic field, can rotate very fast
Arrange in order from smallest to biggest: The Sun, the Milky Way, Earth, neutron star, the Moon, the Small Magellanic Cloud, Coma galaxy cluster, Orion nebula
Neutron Star, The moon, Earth, The Sun, Orion Nebula, Magellanic Cloud, Milky Way, Coma Galaxy
Neutron Star Size, Parent star, Mass limit, what happens if it reached its mass limit
Neutron Star: 10-29 Solar Masses Size: 1.4 solar masses Maximum mass limit: 2.1 Solar masses What happens if the mass exceeded? Black Hole
Can.a theory be proved?
No, Theories can only be disproved
If someone said I'm going to use the redshift of that star in the galaxy to measure how far away it is, would that be a good way to measure distance?
No, because the redshift will describe its velocity
Would you expect to see a last quarter moon in the sky at sunset?
No, it sets at noon
Is our Sun expected to go supernova in the future? Why/why not?
No, our Sun is not expected to go supernova. When it is a white dwarf it would need to be kicked over the Chandrasekhar mass limit (1.4 solar masses) which could only happen if it collides with another white dwarf (unlikely) or accretes mass from a binary companion (which it doesn't have).
Hyperion (Saturn)
Non circular orbit due to gravitational effect of Titan. It has chaotic rotation (Tumbles over its elves and have no fixed rotation axis or period
Proper (Transverse) component
Not moving toward or away Component transverse relative to the sun (corrected for parallax) measured in Arcsec/year
1 Solar Structure: Core
Nuclear Reaction
What comets made of?
Nucleus is similar to asteroids and included dusty trapped in mixtures of methane, ammonia, carbon diode, and dirty ice
Frequency (F)
Number of wave crests passing a given point per unit of time (1 per sec = 1 Hertz = 1HX F=1/P
Saturn's internal structure
Outer Crust: Molecular Hydrogen Mantle: Metallic Hydrogen Core: Icy. Rock Saturn has a much smaller metallic hydrogen layer than Jupiter
Jupiter's internal structure
Outer Region - Gaseous Inner Region - Liquid Core: Icy/rocky core Lower Mantle: Metallic Hydrogen
Explain why volcanism on Earth is important for sustaining life on the planet?
Outgassing from volcanoes increases the carbon-dioxide in the atmosphere, contributing to the greenhouse effect which keeps the planet warm enough to sustain liquid water.
P waves
P-waves are Pressure waves and are longitudinal. They can pass through all media
orbital period
P^2=A^2/M
celestial coordinates
Pair of quantities right ascension and declination similar to longitude and latitude on Earth, used to pinpoint locations of objects on the celestial sphere.
EM Radiation: Radio Applications
Penetrates dusty regions - Applications: Magnetic Fields, interstellar gas clouds, galactic structure, active galaxies, cosmic microwave background radiation
EM Radiation: Infrared Applications
Penetrates dusty regions, atmosphere is partly transparent Applications: Star formation, cool stars, AGN, center of Milky Way, large scale structure
Mars moons
Phobos and Deimos
What science can you do with an image?
Photometry = Measurement of the brightness of objects Photometer= can measure total light per unit time to see changes in intensity
Radiation Era
Planck Epock ~0-10^-43second - Current physics can't tell us what happened during this time GUT (Grand Unified Theory) Eopch: 10^-43 - 10^-35second - Electromagnetism, weak & strong forces still unified (gravity decoupled) Quiarks and leptons - 100 second - Building blocks for protons, neutrons & atoms Nuclear Epoch: 50000 years - Hydrogen fusion to create the primordial HE - Radiation still dominated over matter
Exoplanets
Planets around tars that ate not the sun
What is the scientific method?
Process - Observe,Make a model, Make a prediction, iterative
Stage 4: A Protostar
Protostar central Temp ~ 1 million K (ionised gas but not hot enough for nuclear fusion yet) • size ~ Mercury's orbit• surface Temp ~ 3000 K L = 4πR2σT4 • luminosity totally driven by release of gravitational energy as protostar continues shrinking • as the protostar shrinks, it spins faster and a protostellar disk may form around it (if planets are going to form, they will be well on their way!) - Once the star has become a protostar with a photosphere we can start to plot its location on the H-R diagram. A sun like star will enter the H-R diagram at point 4 and will evoke to move to different locations
stellar motion Components
Radial Motion & Proper (Transverse) Motion
Energy is transported in the sun in what two ways?
Radiation and Convection
Radiation (Photons) take how long to reach earth?
Radiation move at c=3x10^8 m/s 8 minutes
Why the Milky Way is a spiral galaxy
Radio observations (21 cm radiation) of neutral hydrogen gas clouds in the Galaxy have allowed astronomers to mat out the spiral arms - Radio radiation not affected by dust extinction
The Solar Neutrino "problem"
Raymond Davis tried to study Neutrinos by having a tank filled with Chlorine to see if parts of it would convert to Aragon. The problem was that they only managed to count about half of the number of neutrinos that they were expecting as predicted by the standard solar model
The Hubble Constant
Recession V=h0 x distance h0= 70 km/s/mpc The Hubble constant is the constant is the constant of proportionally between the recesssion velocity and the distance - h0 specifies the expansion rate of the universe - there is still uncertainty (measuring how fast the universe is expanding)
What 2 effects are caused by the dust in the Interstellar Medium on starlight?
Reddening & Interstellar extinction
Nicolaus Copernicus
Rediscovered the Heliocentric system (sun- centered).
Which of the following stars is furthest from us?
Regulus (parallax angle = 0.04 arcsec)
Tulley-Fisher Relation:
Relationship between the brightness of a spiral galaxy and its rotation velocity
Longitude (E or W)
Right Ascension (RA) (hours, min, sec)
The Discovery of Uranus's Rings
Rings discovered in 1977 from ground based observations using stellar occupation - Astronomers studied the components of its atmosphere by taking a spectrum of the background star's light as it passed through Uranus's atmosphere
At approximately what time would a full moon rise/set?
Rise 6pm, set at 6am
First probe landing on a comet ever?
Rosetta Mission- Landed a probe on Comet 67p (2014)
S waves
S-waves are Shear waves and are transverse waves. They do not travel through liquid ( they are absorbed)
Spiral galaxies are diveded up into 2 sub classes
Sa - Sb - Sc Big to small
Which of Galileo's initial observations was most challenging to established geocentric beliefs?
Satellites of Jupiter. - Seeing 4 moons clearly move around Jupiter disproved that everything orbited Earth and showed Earth could orbit the sun and not lose its moon too.
What is the name of the radius at which nothing, not even light, can escape from a black hole?
Schwarzschild Radius
N-body simulation
Scientists have built detailed computer simulation to model the gravitational interactions and gas dynamics
a) Explain how you would identify if a galaxy is active or not. [1]
Several Answer Options: - Observe the galaxy at radio frequencies and look for jets and lobes (radio galaxy) -Observe the galaxy at infrared frequencies and look for much brighter than normal emission from the centre (Seyfert) -Observe in X-ray or gamma-ray frequencies and look for bright emission from the centre (e.g. blazar) -Observe its spectrum and notice that the spectral lines are much broader than usual -Observe that the total luminosity is much higher than for normal galaxies (L>10^37 W)
Ceclia Payne-Gaposchkin
She showed that stars are composed mainly of H & He but was forced to weaken this statement in her PHD by Russell because it went against commonly accepted views!
What causes large clouds to start collapsing?
Shock Waves: = shell of gas rushing through space. Shockwaves push normally thinly distributed matter into dense sheets. The sudden high density can cause gravitational collapse to start.
SKA Observatory Treaty sign info
Signed in Rome on Tuesday 12, March 2019
Color Index
Simple numerical expression that determines the color of an object, which in the case of a star gives its temperature. The smaller the color index, the more blue (or hotter) the object is. Color Index = B-V B (Blue Filter) V (Visual)
Where did Moon come from? Theories
Sister/ Conformation Theory Capture Theory Daughter/ fission theory Impact Theory
Type of Merger (3) possible elliptical galaxy
Size and mass of sick Galaxy A ~ Size and mass of Galaxy B Possible destroys spiral galaxies disk and creates starburst event - eventually may end up an elliptical galaxy
terrestial planets
Small, dense, & solid Has a thin crust Silicates mantel Liquid Iron- nickel outer core Solid Iron nickel inner core
Calculate the solar constant
Solar Constant = Luminosity/ 4 PIr^2 r= The distance form sun to planet in meters
Which of these is NOT a form of electromagnetic radiation?
Sound - Sound waves form from pressure waves
How do we measure stellar composition?
Spectroscopy , Take spectrum and look at lines, composition, & temp
Black hole escape velocity
Speed of light, so no light can escape
How do these theories of galaxy evolution conflict with Hubbles ideas about the Hubble sequence
Spiral galaxies become elliptical galaxies - Where there are dense clusters there aren't many spiral galaxies and we believe that they changed form
How do we estimate the masses of galaxies?
Spiral galaxies: Measure Rotation curve Ellipticals & irregulars: Measure velocity dispersions of stars
Stages of Stellar Formation
Stage 1: Interstellar cloud contracts Stage 2: Cloud fragment collapses Stage 3: Fragmentation stops Stage 4: Protostar Stage 5: Protostar evolves Stage 6: Newborn star Stage 7: Main sequence star
Cluster Lifetimes
Star clusters eventually dissolve and stars are left on their own Open Clusters- a few million years to billions of years old Associations: 10s of millions of years Globular Clusters: Stars still found in gobbler clusters which as ~ 10 billion years old!
Types of Star Clusters
Stars form in clusters Open cluster: • irregular clusters • ~100s - 10 000s stars • few pc across Association • less massive but more extended• a few 100s stars• many 10s pc• rich in young stars: • T associations (many T Tauri stars)• OB associations (many O- & B-type stars) Globular Cluster • spherical shape• 100k - millions of stars • ~50 pc across • contain old stars with low abundance of heavy elements
Intrinsic variable Stars
Stars that are intrinsic variable stars - Pulsating stars Names: - RR Lyare (0.5-1 day) - Cepheid Variables (1-100days_
variable stars
Stars whose brightness appears to fluctuate - Eclipsing binaries - novae & Super novae -Cataclysmic WE ARE TALKING ABOUT INntrinsic variable stars
Dwarf Stars are
Stars with R<= Rsun
Stage 1- An Interstellar Cloud
Start with a dense interstellar cloud (dark dust cloud or molecular cloud) which collapses and fragments... • Interstellar clouds vast: 10 - 100 pc across and very massive • Temp ~ 10 K (cold, but still enough to balance gravity) • To start the contraction / collapse, need an external event to create an instability: • shock waves from supernovae• pressure waves from very bright O or B stars
Formation of Matter
Started through pair production - Two photons have high enough energy (gamma rays) and these photons interact with each other and through the interaction create two particles If they interact they can annihilate each other
Dark matter candidates
Stellar candidates (MACHOS (massive compact Halo objects) ) - Stellar mass black holes -brown dwarfs (pre-stellar objects which never began H- burning) - White dwarfs - Faint, low mass red dwarfs (unlikely from globular cluster measurements) Sub atomic Particles: - WIMPS (weakly interacting massive particles) Must be massive to interact gravitationally, but not interact with normal matter in any other way Modified gravity: - Perhaps gravity behaves slightly differently on very large scales (but not likely)
proton-proton chain Steps
Step 1: (proton fusion), the same reaction is taking place all through the core of the Sun, with protons fusing to form deuterium. Step2: (deuterium fusion):A deuterium fuses with a 3rd proton to form He plus some energy is released. This reaction also happens throughout the core. At this point we 3 have used up 3 Hydrogen nuclei(protons) to form a He nucleus. Step3:(He-3fusion) :two He nuclei (each formed from 3 Hydrogen nuclei) fuse to form a He nucleus and release two Hydrogen nuclei and some energy in the process.44 Therefore, the net number of hydrogen nuclei used to form a He nucleus-is 6-2=4. Therefore overall, 4 Hydrogen nuclei a reconverted to1 He nucleus and produce energy during the process.
Explain how you would use the Hubble-Lemaitre law to measure the distance to a distant galaxy: describe each observation/measurement and calculation you would need to make after you had decided on your target galaxy.
Step 1: Observe a spectrum of the galaxy with my telescope Step 2: Find the redshift of the galaxy by comparing the spectral lines in the spectrum with their rest positions Step 3: Use the Doppler formula to calculate the recession velocity of the galaxy Step 4. Use the H-L law (v = H0xd) to calculate 'd' since H0 and v are known.
Neap Tides
Sun & moon at right angles to earth - Little variation between high and low tides (lower high tides and higher low tides)
Super giants are
Super Giants are stars with 100 Sun <R< 1000 Rsun
4 Solar Structure: Photosphere
Surface of Sun which we see
Solar activity: flares
Takes place in lower atmosphere near active regions, flash across sun in minutes -Release huge amounts of energy and highly energetic charged particles which are blasted into space - X ray & UV Radiation
The frequency at which an object's (e.g. a star) intensity is greatest depends directly on its
Temperature
The E Ring (Saturn)
The E Ring also contains a moon, Enceladus. Enceladus has volcanic eruption which are likely the cause of the material in the E ring
Moon Tidal Lock
The Earth's moon is tidally lacked to the earth, which means that its rotation and orbital period are the same (always show the same face to the Earth). - Called a 1:! spin orbit resonance
Given that Earth is much larger and more massive than the Moon, how does the strength of the gravitational force that the Moon exerts on the Earth compare to the gravitational force that the Earth exerts on the Moon?
The Forces Are The Same F=GMm/r^2
Spectral Classification
The Harvard system from hottest (60 000K) to coolest (2 000K) is O-B-A-F-G-K-M (Stars spectral type)
The name of the region where planetoids like Pluto reside
The Kuiper belt
Why does the Milky Way not have enormous radio waves?
The Milky Way is not an active galaxy because it is a stable galaxy and nothing is falling into the black hole in our galaxy
Earth and the Moon are thought to have formed close together in time - the Moon likely from part of the Earth's material. However, these two bodies have very different surfaces - the Moon has thousands of visible impact craters, with a wide range of sizes while Earth only shows a few large craters. Which of the two objects (Earth or the Moon) has the older surface, and explain why the appearance of cratering on the surfaces of these two bodies is so different from each other?
The Moon has the older surface (even though it was formed from the Earth's material!) (1) The Moon has no atmosphere which means that all incoming meteoroids will impact its surface whereas the Earth has an atmosphere which stops smaller meteoroids reaching the surface as they disintegrate due to friction in the atmosphere. (2) Except for micrometeoroids impacting the surface and eroding surface features on a very long timescale, the Moon has no other erosion processes to cover over cratering. The Earth has flowing liquid water which erodes cratering and other surface features on a much shorter timescale, thereby erasing craters.
Pan moon (Saturn)
The Ravioli Moon
Temperature Scale
The SI Unite of temperature is the Kelvin (K) 0 degrees celsius= 273K -273 degrees celsius = 0 K - All thermal atomic and molecular motion ceases
Solar Structure Diagram
The Sun has 7 layers. We see the photosphere layer which is the layer that emits the radiation (light) that gets to our eyes. (photo = light, sphere = sphere: so photosphere is the sphere from which the light comes).
The Solar Constant
The amount of solar energy reaching the top of Earth's Atmosphere per second =1400 j/s/m^2 =1400 w/m^2
Intensity
The amount or strength of radiation at a point in space - Any object with a non-zero temperature emits radiation distributed over a range of frequencies
The Modern Magnitude Scale
The astronomical brightness scale; the larger the number, the fainter the star. Created by Hiparchus in 2nd century Rank 6- Dimmest 1- Brightest 1 is 100x brighter than 6th mag star with 2.5 difference between each number Change in 5 magnitudes DEFINED as a change in apparent brightness of a factor of 100
EM Radiation: Ultraviolet applications
The atmosphere is opaque, space based observations only Applications: Interstellar medium Hot stars
The aurora (the northern or southern lights)
The atmospheric molecules are excited by the collision when they drop down to lower energy levels, they release photons which we see as the aurora.
Barred Spirals
The bar extends out of the central bulge and the arms start at the ends of the bar. Halo - Old faint stars Central bulge- with high stellar density (galactic nucleus) Bar - from bulge into disk containing stars and ism Disk - Most light from A-G stars - Right in mass looks white/blue
Why can't astronomers use simultaneous observations from different parts of Earth to determine stellar distances?
The baseline is too small
Light & Telescope size
The bigger the collecting area, the more light can be collected
The central supermassive black hole
The black hole is not the source of the energy we see Rather, the matter it is accreting (in a large accretion disk) emits energy as it falls into the black hole - The accretion disk also has strong magnet fields which can accelerate particles to very high energies which we observe on earth as cosmic rays
Luminosity
The true brightness... How much energy it radiates in all directions per second (THE INTRINSIC BRIGHTNESS)
The virgo cluster
The closest large concentration of galaxies to the local group is the virgo cluster
Halley's Comet
The comet discovered in 1705 by Edmund Halley that has an orbit which brings it back to the sun every 76 years and last appeared in 1986.
solar wind
The constant stream of particles leaving the sun (Not a layer of the sun) Photons and fast moving protons and electrons (the parts of hydrogen atoms) are escaping from the sun all the time.
The Crater Chains
The crater-chain is likely made up of domes created when lava upwelled and which then collapsed when the lava receded
umbra
The darkest region of a sun sport is called the umbra
Wavelength
The distance needed for a wave to repeat itself (peak to peak/ trough to trough)
Explain what an astronomer means if they tell you that the seeing last night was 1 arcsecond.
The distortion to images due to atmospheric turbulence would smear out objects over a resolution of 1 arcsecond. -You would only be able to tell two objects apart if they were separated on the sky by more than 1 arcsecond.
The photoelectric effect
The emission of electrons from a metal when light shines on the metal... -+- Light doesn't only behave like a wave it also seems to have particle properties E=H*F H= planck's constant H=6.63 X10^-34 J.s
Where in the sun spot cycle is the sun if I notice that the sun spots are forming near the equator?
The end
Electromagnetic (EM) Radiation
The energy is transmitted by fluctuating electric and magnetic fields For this course: EM Radiation = Light
Irregular Galaxy
The galaxies that don't fir into any of the categories & don't have regular structures. -Rich in ISM and young. blue stars - Lack regular structure 2 types of irregular galaxies - IRR I: Misshapen Spirals - IRR II: No coherent or regular structure at all - looks explosive
"Seeing" in astronomy is a measurement of
The image quality due to air stability "Good Seeing" occurs when the atmosphere is clear and the air is still
Titan (Saturn)
The largest of Saturn's satellites, Titan might be the largest satellite in the solar system, It is the only satellite to have a substantial atmosphere. Its significant atmosphere, a mix of nitrogen (80%), methane (20%), and argon (trace), also makes it unique among satellites. - Lakes of liquid methane - Liquid water under the surface
Penumbra
The lighter dark region around the sun spot
Local Supercluster
The local supercluster ia also known as the Virgo super glister and includes the local group, the virgo cluster, and various clusters located about 20-30 npc from virgo (tens of thousands of galaxies)
zero-age main sequence (ZAMS)
The location in the H-R diagram where stars first reach stability as hydrogen-burning stars Stars DO NOT evolve onto the Main sequence rather they move onto it and off as the star evolves
Magnetosphere (of Earth)
The magnetic field around Earth which deflects charged particles travelling from the Sun.
spectroscopic parallax
The method of determining a star's distance by comparing its apparent magnitude with its absolute magnitude, as estimated from its spectrum. - Observe a star's apparent brightness - Observe the star's spectral type and find where it lies on the main sequence of the H-R diagram = estimate the luminosity
Sister/ conformation theory
The moon formed as a separate object near the Earth at about the same time (I.e. formed as a double plate system) BUT... not likely because the moon has a different density and composition to earth
Capture Theory
The moon formed far away from the Earth but was eventually pulled in, or captured by the Earth's gravitational pull. BUT... not likely because of their size differences and also there are similarities between objects
solar maximum
The number of sunspots on the sun at one time reached a maximum approximately every 11 YEARS
Kepler's First Law
The orbit of each planet around the Sun is an ellipse with the Sun at one focus.
The Corona
The outer layer of the sun's atmosphere. Only seen during solar eclipses which obscure photosphere and chromosphere. Spectral lines are completely different from photosphere: - Emission not absorption Highly ionized elements imply high temperature of corona
apogee
The point in the moon's orbit where it is furthest from earth
Perigee
The point in the orbit at which the moon is closest to the earth
What is the difference between the sun spot pairs in the North vs the sun spot pairs in the South
The polarity is opposite
Solar Magnetism
The powerful magnetic field of the sun (discovered by George Ellery Hale, 1980)
What is extinction?
The process where light is blocked by dust
Telescope Purpose
The purpose of the telescope is to collect and focus light
Hubble- Lemaitre Law
The rate of recession of a galaxy is directly proportional to its distance form us Formule --- Recession velocity = h0 x distance Vesto Slipher notices in 1917 that almost all galaxy spectra he observed were red shifted - were all moving away from the Milky Way. - Individual galaxies (not in cluster) are moving away steadily - Galaxies in clusters have random motion direction but: - The overall motion of a galaxy cluster also is away from the Milky Way - The greater the distance, the greater the red shift
Why galaxy look redshifted
The redshift we see in the spectra of distant galaxies is due to the expansion of the universe (the galaxies themselves are not moving away from us at high velocity and those photons are being stretched out. NOT A DOPPLER SHIFT
period-luminosity relation
The relation that describes how the luminosity of a Cepheid variable star is related to the period between peaks in its brightness; the longer the period, the more luminous the star. Apparent Brightness = Luminosity/ Distance ^2 Relation found by Henrietta Leavitt (1908)
Stefan-Boltzmann Law
The relationship stating that an object emits energy at a rate proportional to the fourth power of its temperature, in Kelvins.
Saturn's rings
The rings were observed by Galileo and Huygens in 1600s JC Maxwell proposed in 1857 that they were made of many small particles orbiting Saturn individually - mainly composed of ice and are very reflective - Small gaps in the rings due to moonless which sweep up the particles as they orbit!
Dark Matter
The rotation curve of the milky way implies that there must be much more matter in our galaxy than we can see (i.e more than the luminous matter and gas that we observe) -Dark Matter has not be detected at any EM wavelengths, only seems to interact gravitationally
Homogeneous
The same everywhere/smooth on the largest scales
From the smallest to the biggest, the correct order is
The solar system, Milk Way, Great Walls
dynamo theory
The spin of the Earth coupled with the liquid metallic core causes the magnetic field we observe (the liquid metal (a conductor) moves around inside the core due to Earth's rotation and thereby creates a magnetic field) Remember: Accelerating electric charges generate magnetic fields
Kepler's Third Law
The square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit.
How does the temperature of a star near the bottom left of the H-R diagram compare with a star of the same luminosity near the bottom right of the H-R diagram?
The star near the bottom left has a higher temperature
Spring Tides
The sun & moon aligned with earth - Highest high tides & the lowest low tides
Describe the structure of the Sun, its different layers and energy generation and transport mechanisms. Also explain and describe the evolutionary stages the Sun is expected to go through as it leaves the main sequence until its expected final state.
The sun is made up of - The chromosphere, photosphere, convection zone, radiative zone, and the core ()The corona is the outermost part of the sun () The chromosphere is a layer of the sun's outer atmosphere. () Photosphere is the lowest layer of the sun's atmosphere. ()Convection zone is made entirely of plasma that is sending heat up to the sun's surface () Radiative zone is the one around the core and it produces gamma rays and x-rays that move the core's heat energy out toward the surface () The Core is the center of the sun. This is where all the sun's energy comes from The Evolutionary stages of the sun In 4.6 billion years the sun will turn into a red giant, use up its helium, and as it evolves with turn into a white dwarf Main sequence to hydrogen shell fusion (higher hydrogen fusion) then Sub Giant, Red Giant, then white dwarf
How did the geocentric model account for day and night on earth?
The sun orbited earth
Total exlipse
The sun, moon, and earth perfectly alined + be in umbra
Impact Theory
The theory that the moon was created from materials ejected when a large object struck the earth
progenitor
The thing that gave rise to/came before (ancestor)
Local Solar Time
The time according to the position of the sun in the sky relative to one specific location on the ground.
Synodic Month
The time between new moons - 29.5 days
What does the Hubble flow imply?
The universe is expanding. The space between the galaxies are becoming bigger with time . - Only on the largest scales is the universe expanding (the vast distances between galaxy clusters) NOT: The solar system, stars, planets, etc. - These things are held together by internal forces and gravity
The cosmological principle
The universe is homogenous and isotropic on the largest scales
Where did the Big Bang take place?
The universe started as a point and then expanded = BUT it did NOT explode better into empty space = Rather, space and time themselves (ie. the universe itself) expanded from a point - There is no special place in the universe- it is homogenous
Granulation
The visible surface of the sun appears mottled/granulated. Brighter (Moving upward) = Hotter Darker (Moving downward)= Cooler
What is omega zero
Theoretical studies have suggestion that the universe has to be flat (1) - but when compared to observable findings and dark matter we get ~.25 - We only know 96% of the universe
Implications of Homogeneous & Isotropic
There can be no edge to the universe, and there can be no centre to the universe.
Volcanoes on the moon
There is evidence that the moon had volcanic activity but stoped billions of years ago. - Crater-chain most likely due to volcanism (underlying fault where lave could well up from below. - Maria (not much cratering) likely from volcanic flows - Volcanic Rilles: Ditches where lave once flowed
Janus and Epimetheus ( Saturn)
They are in very close circular orbits: When the inner moon laps the outer moon, the outer moon gets kicked into the inner orbit and the inner moves to the outer orbit. They continually swap over like this over time.
Pulsating stars
They are not on main sequence, They live in the instability strip on the H-R diagram. - High mass stars - upper section: Cepheids -Low Mass- Horizontal Branch stars: RR Lyare
Spiral Galaxies Color
They are usually blue in color because they contain IDM which allows for new stars to form. The recently formed high luminosity O and B type stars give the disk the blue/white color.
Sun Spot and magnetism
They come in Paris and have opposite magnetic polarity. Sun spots have opposite polarities in S & N hemispheres
Spiral Galaxies
They have a central bulge and a disk with spiral arms. They will also have also (like the Milky Way) but these are too faint to observe here. -Central Bulge: High Stellar density, highest in the center is the galactic nucleus - Disk - Mot light form a-g stars, rich in gas and dust for continued star formation (appear blue/white)
The star Rigel is about 1000 times more luminous than the Sun and belongs to spectral class B8. Sirius B is about 1/3000 times as luminous as the Sun and belongs to spectral class B8. Which star has the greatest surface temperature?
They have the same temperature
Telesto, Tethys, Calypso (Saturn)
They share the same orbit, but are offset by each other at all times by 60 degrees at the stable langrangian points in the orbit
Ancient Greek Astronomy
They were the first to use scientific methods to model the universe 3 main observations: - Retrograde motion of the planets (planets = wanderer) - The sun moves relative to the stars across the sky over the course of a year (along the ecliptic) - The planets are bright at some times and dimmer at others
Galactic Bulge
Thick distribution of warm gas and stars around the galactic center
How do we measure stellar masses
Through observing gravitational interactions with other objects
What 2 methods can we use to measure the temperature of a star?
Through the black body curve or spectra lines
hydrostatic equilibrium
This means that the inwards pressure from gravity is balanced from the high temperature of the gas. For example: The sun is staying the same size and isn't shrinking or expanding
The moon is
Tidally Locked, We always see the same side towards earth
One 1 Solar Day
Time form noon on one day to noon on the next day
Venus - Noon to Noon
Time from noon to noon on Venus is 117 days. So 1 day on Venus is 117 each days (half a Venus year)
Tropical year
Time it takes from one vernal equinox to the next (365.2422 mean solar day)
Micrometeoroids
Tiny rock fragments no larger than sand grains that travel through space - If they intersect with Earth's orbit, then we will experience a meteor shower when they streak through the atmosphere
Saturn's largest moon
Titan
Red shift surveys in the 1980s to see how big super clusters could go.
To find how big these super clusters could go astronomers in the 1980's stared doing red shift survey. They started measuring the ---- -spectra if distant galaxies - measuring the recession velocity of those galaxies, and using the -Hubble- Lemaitre law to calculate the distances we see that galaxy distribution is not random! Galaxies are arranged in networks/filaments/strings surrounding vase open spaces called voids - think of huge soap bubbles with galaxies on the surface ---- Great wall - 1 of largest known structures (200 mpc)
Given our current observations, our universe is expected to continue expanding forever
True
Gravity is only a theory
True
Lower mass stars live longer on the main sequence than higher mass stars.True / False
True
More massive stars form faster than less massive stars.
True
Urey-Miller experiment (1953) findings
Took a mixture of H20, methane, c02 Nh3, and sent electrical discharge through it (like lightning) - Few days later found amino acids had formed
Calculate how many times the comet can orbit the sun before its material will completely evaporate away
Total Mass/ Mass it looses
Van Allen Belts
Two doughnut-shaped regions 1,000-25,000 kilometers above Earth that contain electrons and protons traveling at high speed. - Earth's magnetic field causes charged particles to spiral around the field lines. Sometimes participles escape the belts at the poles and enter the atmosphere which cases Aurorae at high or low latitudes. The belt shields us from the sun's wind and flares
Types of Supernovae
Type 1: H - Poor: -Detonation of a carbon white dwarf (why there is no H!) -Light curve due to radioactive decay of heavy elements created in the explosion Type 2: H - Rich: - Rebound from the core collapse of a massive star - Light curve due to expansion and cooling of the star's outer envelope (lots of H) () All High mass stars go to Type II supernova () But ONLY some white dwarfs go super nova
Super Nova Light Curves
Type 1: Hydrogen- poor, similar light cure to Novae Type II: Losts of hydrogen, light curve plateaus (flattens out)
2 types of supernovae
Type 1: carbon detonation supernova, progenitor=white dwarf (that goes over the Chandrasekhar limit) Type 2: core collapse supernova, progenitor = massive star (>8 solar masses)
Two types of supernovae
Type 1: carbon detonation supernova, progenitor=white dwarf (that goes over the Chandrasekhar limit) Type 2: core collapse supernova, progenitor = massive star (>8 solar masses)
Elliptical Galaxies color
Typically contrail older evolved stars (red giants) because there is no ISM to give rise to new stars.
Southern Hemisphere
Vernal Equinox - March 21 S.H. Winter Solstice- 22 June - Highest North Point, Longest day S.H Spring Equinox - 21 September S.H Summer Solstice - 22 December - Highest South Point, Longest Day
Refractor Telescope
Uses lenses to focus incoming light
Reflector Telescope
Uses mirrors to focus incoming light
Swartzchild radius
V esc=C A black hole is an object which lies within its own R
Mercury's interior
Very large, iron-rich core
What types of Electro-Magnetic Radiation from space reach the surface of Earth?
Visible light & radio Waves
absorption lines
Visible lines on an observed color spectrum that reveal the chemical composition of the light source
You notice the moon directly above you at 9am. What phase is the moon?
Waning Crescent
dirty ice
Water Ice with trace amounts of ammonia, methane, etc
The distance between successive wave crests define the _______ of a wave
Wavelength
Utilizing the Imagine technique
We are able to find massive planets far from their host stars because we need to be able to resolve them as separate with our telescopes and for large planets too close to their stars this would not be possible. - small planets are too faint to detect - we assume there are only large planets
If you look overhead at exactly the same time of night on 2 successive days, why do the stars appear slightly shifted compares to the previous night?
We are not only rotating on our own axis, but we are also rotating around the sun.
Star: Indirect Measurements
We can measure Luminosity, L L= 4 Pi R^2 * (5.67 x 10^8)T^4 4piR^2 (Surface Area) 5.67 x 10^-8 (Stefan-Boltzman Constant)
When we compare values of apparent magantide
We can use brightness
When we compare values of absolute magnitude
We can use luminosity
Measuring the Cosmic Expansion
We expect that although the universe may continue to expand forever that rate at which it expands should be slowing down. - If its slowing down then we would expect distant objects to appear to be receding faster than Hubble's Law predicts. We do this by: Measure the redshift and distances of the galaxies in an independent way. Measure an independent distance and indecent red shift. in other words - if the universe was expanding faster in the past this is how you'd expect to measure the deceleration of the universe BUT they were actually found that the Universe was accelerating not decelerating
Large scale structure
We know that galaxies tend to be found in groups and clusters but we also found that galaxies in clusters also cluster themselves in SUPER CLUSTERS
Radiation density
We look at the cosmic microwave background, radiation, and you can convert the energy of those photons into a equivalent mass using E=mc^2 and divide it by the volume of the universe back in the day where the volume was much smaller then there would be more energy in photons than in mass.
What evidence supports the idea that the Sun reverses the direction of its magnetic field approximately once every 11 years?
We notice that during each sunspot cycle, the magnetic polarities of all sunspot pairs per hemisphere are orientated in the same direction - i.e. the leading sunspots all have the same polarities (and are opposite for the two hemispheres) due to the Sun's magnetic field getting twisted from differential rotation. Every 11 years, when a new sunspot cycle starts, the polarity of leading sunspots is seen to be opposite to the previous 11 years indicating that the Sun's magnetic polarity must have reversed.
With such low densities of gas and dust, who do we still see extinction and reddening?
We still observe extinction and Redding because the vast distances between stars mean that there is still a lot of matter to pass through even it its low density.
How do Black holes fit in this picture
We think that every galaxy has a massive black hole. For normal and active galaxies, bigger galaxy mass, bigger black hole mass
Why do we use the tropical year instead of the sidereal year?
We use the tropical year so that we keep our calendar aligned.
How can a lower mass star get to evolve before a higher mass star?
What could have happened is that the system started off with a high mass (blue giant) star and a low mass (solar mass) star in the binary pair and well inside their Roche Lobes - I.e a detached binary system - The high mass blue giant star would have started to evolve off the main sequence first because it would have used up the hydrogen in its core faster
Solar Minimum
When the number of sunspots reached a ver small number or zero
Why are there roughly equal numbers of both kinds of super nova when ever are far more low mass stars in the galaxy than high mass stars?
While all high-mass stars explode as super novae, only a fraction of white dwarfs, in special circumstances, will explode and it works out to be about 50/50 of each type.
White Dwarf Size, Parent star, Mass limit, what happens if it reached its mass limit
White Dwarf: Mass range of parent star - 8-10 solar masses Size: A little bigger than earth Maximum mass limit: 1.4 Solar Masses What happens if the mass exceeded? Type IA Supernovae
White Dwarf Mass Limit
White dwarf mass limit = Chandrasekhar Limit = 1.4 Msun
The future:TESS - Transiting Exoplanet Survey Satellite (2 years)
Will survey 200 000 brightest stars near to the sun. expecting to find ~ 300 earth like planets over 2 years of observing (April 18, 2018 - run for 2 years) Found 45 confirmed planets and 1799 candidates
A telescope searching for newly formed stars would make the most discoveries if it were pointed
Within a spiral arm
How do we investigate the interior of the sun?
You can make observation, spectrum, make a theoretical model and test it against our observation
How to use the southern cross to find south
You draw an imaginary line through the longest angle of the southern cross from the top all the way to the ground. - Then find the mid point between the two pointer stars and draw an imaginary line through it all the way to the ground - They place where those two intersect draw a line to the ground and that is south
Active Galaxy are
Younger Galaxies
Novae
a close binary star system consisting of a white dwarf and a newly formed red giant will result in the formation of an accretion disk around the white dwarf.
Molecular Cloud
a cold cloud of dust and gas dense enough to form stars Found in darkest dusted regions. - Dust helps to shield molecules from energetic radiation - Dust might be catalyst for molecule formation Molecular hydrogen (H2) is most abundant molecule in molecular clouds but does not emit Radio radiation.
dust tail
a comet tail caused by dust particles escaping from the comet's nucleus. Broad, diffuse and gently curved - Strongly influenced by sun's gravity and follow the orbit (Slightly curved)
Maunder butterfly diagram
a graph showing the latitude of sunspots versus time, first plotted by W.W. Maunder in 1904
Positron
a particle with the mass of an electron but a positive charge
Meteoroid
a relatively small, rocky body that travels through space. Any meteoroid/ asteroid which make sit to the surface of the earth is called a meteorite - Most meteorites are old (4.4 - 4.6 billion years old)
igneous rock
a type of rock that forms from the cooling of molten rock at or below the surface
annular eclipse
an eclipse of the sun in which the edge of the sun remains visible as a bright ring around the moon.
The wavelengths of the emission lines produced by an element
are identical to its absorption lines
Volcanoes on Mars
are much larger than on Earth, Olympus Mons (700km across and 25 km high) - All volcanoes are shield volcanoes - has over 100 volcanoes - not clear it they are still active
Quasar spectra
are strongly redshifted
coronal holes
areas of low density in the gas of the corona from which particles escape (solar winds)
What type of galaxy is the Milky Way?
barred spiral
Diffraction is the tendency of light to
bend around corners and edges
emission lines
bright lines that are made when certain wavelengths of light are given off, or emitted, by hot gases ++ When hydrogen gas is energized it gives rise to light only at specific wavelengths or frequencies -=-=- Each element emits lines at specific and different wavelengths( unique fingerprints)
If light-gathering power is proportional to the area of a telescope's mirror/lens, how much fainter an object could one see with a 5m telescope vs. a 1m telescope in the same time? observed brightness ∝ collecting area (= πr2)
brightness (1m) ~ pi times 1, brightness (5m) ~ pi times 25 —> 25/1 = 25 times
Compared with the orbits of short-period comets, the orbits of long-period comets
can come from all directions
speed of light
c = 2.99 x 10^8 m/s
Cold Neutral Gas Cloud
can Measure in radio telescope Measure densities and temperatures of the dark clouds using 21 cm emission line from H
Why do some glaxies not have cepheids?
cepheids live in the instability strip on the HR diagram and some galaxies maybe older and no longer have cepheids.
What would ht emotion of the stars look like at 30 degrees south on earth?
combination of rising and falling and some are always visible
Apollo asteroids
cross Earth's orbit
Amor asteroids
cross Mars orbit
Uranus's rings
dark, contain little dust, confined by small moons. discovered during an occultation when Uranus crossed in front of a star there are 13 rings that go up & down on Uranus - Uranus also has shepherd moons (Cordelia & Ophelia) which stop its rings diffusing or spreading out (gravity DUH)
Johannes Kepler (1571-1630)
developed laws of planetary motion
A total Lunar eclipse occurs
during the full moon phase
Every two times Earth's Moon rotates on its axis, it orbits Earth
exactly two times
Globular clusters are mainly found
galactic halo
Emission Nebulae
glowing clouds of hot interstellar matter - Hot star (O or B type) inside the nebula ionize the gas with their UV radiation and when the atoms recombine, the gas glows (fluoresces) - typically RED due to H-alpha Emission
Precession is caused by
gravitational pull of the sun and moon
C-type asteroids
high carbon content or 'carbonaceous', 75% of known asteroids; - Though to consist of very primitive material from earliest stages of solar system - 3 largest: Ceres (949km) , Pallas (580 km), Vesta (540km)
S-type asteroids
high silicon or 'silicaceous', 15% of known asteroids. - Mainly found in the inner part of asteroid belt - more reflective
The main reason that most professional research telescopes are reflectors is that
large mirrors are easier to build than large lenses
Chromosphere
layer of the sun's atmosphere above the photosphere. The chromosphere is very active/solar storms continuously erupting.
sideral day
length of time for earth to complete one full rotation (23 hours 56 minutes)
Traposphere: Venus
lowest layer of atmosphere it's where all weather occurs
distance modulus
m-M = 5 log d - 5 = 5 log (d/10pc)
Converting between absolute and apparent magnitude
m-M=5log(d/10)
Compare apparent magnitude (m) using brightness (b):
m2-m1=-2.5log(b2/b1/) M2 is what you know
Mathematical Relation between m & M Forumula
m=M + 5log(d[pc])-5
What is the absolute magnitude of a star which is 1 pc from earth and has an apparent magnitude of M=1
m=M + 5log(d[pc])-5 m=1+5log(1)-5 =6
Ion Tail
made of gases whose electrons are ionized and giving off light (emission spectra); tail always points straight away from the Sun due to the pressure from the solar wind Comet tails are ALWAYS directed away from the sun
Density
mass/volume
A protostar that will eventually turn into a star like the Sun, is significantly
more luminous
radial velocity
motion toward or away from the observer; the component of relative velocity that lies in the line of sight
Photometry
n. The art of measuring the intensity of light. n. фотометр
Where do stars form?
nebula, gravity collapses on itself
The phases of the moon
new, waxing crescent, first quarter, waxing gibbous, full, waning gibbous, third quarter, waning crescent
Do stars evolve along the main sequence?
no
Sidereal time tells us which line
of right ascension (ra) is directly overhead!
Kepler 3
p^2 = a^3
The tails of a comet
point away from the sun
Interferometry
process that links separate telescopes so they act as one telescope, producing more detailed images as the distance between them increases.
Volcanoes on Venus
produce very large lava flows that cover at least 85% of the planet's surface - Mostly has Shield Volcanoes (unrelated to plate tectonics) Where lava wells up through hot spots fairly regularly and builds up the height of the volcanoes over time - Scientist are questioning is there is still present volcanic activity because - Frequent fluctuations in sox levels in atoms - bursts of radio radiation from regions of surface could be signaling eruptions (like lighting in plumes of earth volcanoes) - could also be the primary reason fro Venus's thick atmosphere
How do pulsars work?
pulsars come from supernova explosions and were likely to be real neutron stars. - 2 hotspots on/above the surface of the neutron at the magnetic poles where high energy particles emit radiation along the magnetic axis - If the radiation happens to be in the right direction, we'll observe the pulars from earth --- As neutron stars spin, they lose energy slowly over time and eventually slow right down.
Types of optical telescopes
reflecting and refracting
Alfred Wegner
scientist who came up with the continental drift theory Active Volcano sites trace out plate boundaries
Suppose the Universe were not expanding, but was in some sort of steady state. How should galaxy recession velocities then correlate with distance? They should:
show a scatter plot with equal numbers of positive and negative recession velocities.
collisional broadening
smearing out of spectral lines because of collisions among atoms of gas
Kepler's Second Law
states that an imaginary line from the sun to a planet sweeps out equal areas in equal time intervals
Stellar Lifetime
stellar mass/stellar luminosity Higher Mass, the shorter its lifetime
Gravitation Microlensing steps
steps: 1: When a foreground star (red) passes in front of a background star, it brightens the light of the background star. The gravitational field of the foreground star warps space to create a gravitational lens that magnifies light. 2. If a planet is orbiting the foreground star, it too, will gravitationally lens the background star for a shorter duration. 3. The astronomer will observe the background star repeatedly over time and look for the signal of it brightening with a large broad peak (due to the foreground star lensing effect) and a small short peak (due to the planet lensing effect).
Wein's Law
the black body radiation curve for different temperatures peaks at a wavelength inversely proportional to the temperature
apparent Magnitude brightness
the brightness of a star as seen from Earth (Symbol: m)
proton-proton chain
the chain of reactions by which low-mass stars (including the Sun) fuse hydrogen into helium 90% of the sun's energy is released by this process 4 hydrogens fuse to one Helium (3 steps)
Roche Limit
the distance a moon can be from a planet before shattering from tidal forces
When multiple radio telescopes are used for interferometry, resolving power is most improved by increasing:
the distance between telescopes
interstellar matter
the gas and dust located between the stars in a galaxy
The Hubble-Lemaitre Law states that
the greater the distance to a galaxy, the greater is the galaxy's redshift
inverse square law
the intensity of radiation is inversely proportional to the square of the distance from the source of radiation
The cosmological principle would be disproved if we found
the observed structure of the universe depends on the direction in which we look
Planets and moons having the most craters have
the oldest surfaces
Cassini Spacecraft
the probe currently studying Saturn and its moons
deferents and epicycles
the ptolemaic model of the universe explained and predicted the motions of the planets with ____ and ____
Asthenosphere
the upper layer of the earth's mantle, below the lithosphere, in which there is relatively low resistance to plastic flow and convection is thought to occur.
Determining Exoplanet properties: orbital period
the time required for a body to complete a single orbit - Measure using transits or radial velocity 1.Semi- Major Orbital Axis: Use keepers 3rd law, using the measured period and estimating the host star's mass 2. Orbital Period: We can use the Radial Velocity Curve period or measure the time between successive transits
Based on our current best estimate of the present mass density of the Universe, astronomers think that
the universe is infinite in extent and will expand forever
The photosphere
the visible surface of the sun, photons can escape freely into space .This is the surface that we see and which produces the black body spectrum we measure/observe. Seen as almost the edge of the Sun
Elliptical galaxy
typically shaped like soccer balls to rugby balls. They are typically very large or quite small and likely have different formation processes between these two types. Central nucleus - where stellar density increases towards center -No disk or spiral arns - little to no cold gas and dust (no on going star formation) - lots of hot gas (x-ray observations)
Galaxies are not
uniformly distributed in space and they tend to group together in groups and clusters
7 Solar Structure: Corona
upper atmosphere, thin & hot
Dark Energy Era
~14 billion years
Stefan-Boltzmann constant
σ = 5.67 x 10^-8 W/m2/K4
Super Nova vs. Nova
• A supernova is more than a million times brighter than a nova • Novae can recur while a star can only go supernova once!
Two ways to create Carbon Detonation Supernovae
• Binary system with accretion onto a white dwarf from its companion • Binary system of 2 white dwarfs which collide to form a massive unstable star with mass > 1.4 Msun -- Both scenarios kick the white dwarfs over the 1.4 Msun limit and Carbon fusion will start, causing the star to explode
Information from spectral lines
• Existence / intensity of lines: Temperature + composition • Shifted lines: Radial Velocity • Width of lines: Rotation, Turbulence, Magnetic fields, density
Pluto
• Orbit inclined to ecliptic plane at 17.2 deg • orbital period: 248 years • orbit crosses Neptune's orbit, but in 3:2 resonance with Neptune, so will never collide • RP ~ 0.2 REarth • Composed mainly of water ice and has frozen methane on surface (~50K)
Astrometry
• This method looks for small changes in position of a star over time which could indicate that it is orbiting a common centre of mass with a smaller and fainter companion • This method has only found 10 exoplanets so far
Spectra from molecules
• electron level transitions [visible & UV photons] (High Energy) • changes in molecular vibration cause photon emission [infrared photons] (medium Energy) • changes in molecular rotation cause photon emission [radio photons] (low Energy)
What causes Shockwaves?
• emission nebulae (hot stars inside the nebula heat them up causing waves of matter to leave the nebula and travel outwards where they collide with interstellar clouds) • planetary nebulae: end point of old stars• supernova explosions: deaths of massive stars (Most energetic and efficient!) • spiral density waves in spiral galaxies-cause gas clouds to contract and increase in density - could start of star-formation this way. • Galaxy - galaxy interactions- if the galaxies get close enough together, their ISM can collide and kickstart star-formation as well.
What are the main differences between a protostar and a main sequence star?
• protostar powered by gravitational contraction while MS stars are powered by nuclear fusion • protostars are not stable - they are still contracting, while MS stars are in hydrostatic equilibrium
Radial Velocity Measurements
•In a solar system (a star with planet/s), the star and planet/s orbit a common centre-of-mass• If you observe the star, it looks as if it is 'jiggling': • the more massive the planet or the less massive the star, the more it 'jiggles' • Astronomers can observe the 'jiggle' as a Doppler shift in the star'sradial velocity measurements (planet is too faint to detect directly)