Physics 127 Final Exam

Scientific vs Spiritual Truth

-"Experiments" -Reliance on experts -Gradual -Objective vs. Subjective -skepticism vs. faith over reason

Random Numbers

-1 light year is the distance light travels in one year -The Moon is only one light-second away -The Sun is 8 light-minutes away -Solar System is about 100 AU in size (AU=Sun-Earth distance) -Nearest star is 1 light year away -Galaxy is 100000 light years across -Earth is 10^4 km across -The universe is 14 billion years old

Chapter 15: The Sun

-100 times larger than Earth, 300,000 times more massive, rotates -75% H, 23% Helium, 2% everything else ("metals") hot enough to be a plasma (fluid of disconnected ions and electrons) -No "surface", but (convecting) photosphere is what we see; surprisingly hot atmosphere on top of that -Magnetic field tangles cause activity: sunspots, eruptions, solar flares, and release of energetic particles + Sunspots are cooler and relatively dark; magnetic field detected in sunspots by changing electron orbits and messing with spectral lines -Solar wind and energetic particles fill solar system, affecting magnetic fields and causing "space weather"; huge storms could be natural disaster, so working on (now-weak) forecasting -Solar activity follows 11ish year cycle

Newton's First Law of Motion

-An object moves at a constant velocity unless a net force acts to change its speed or direction -Conservation of Momentum or Angular Momentum if there is no net force

Chapter 17: Stars

-Brightness = apparent magnitude is a function of luminosity (intrinsic brightness L = R2T4) and distance (inverse square law) + Temperature controls color -Temperature affects the energy of electrons which influences which spectral lines are seen spectral types + All stars are mostly H, a lot of Helium, and a bit of metals -From hottest/bluest to coolest/reddest, spectral types are OBAFGKM; Sun is 6000 K G2 star -Cooler than M stars are brown dwarfs (L,T,Y) which are faint because they never fuse hydrogen -Spectra can also give: radial velocity, detailed composition, clues on stellar size and rotation

Time and Clocks

-Clock's are set to sun's position in the sky, which is different at different longitudes, timezones -The year is approximately 365.24 days, which doesn't line up. So we add an extra day every 4 years to make up for that.

Kepler

-Combined these observations with parts of Copernicus' heliocentric model

Chapter 9: Moon and Mercury

-Earth's geology (volcanism/tectonics) and atmosphere (erosion) erase craters; airless and dead Moon/Mercury retain craters for billions of years -Leftover planetesimals/asteroids/comets are moving very fast: craters are explosions at depth -Know a lot about the Moon thanks to Apollo samples and studies -Two types of surface: darker younger and lighter older -Moon formed in giant impact from the splash of Earth's mantle: explains why Moon has same isotopes as Earth but ~no iron core -Mercury has huge iron core, possibly from mantle stripping impact + Present-day magnetic field means liquid iron outer core

Kepler's Second Law

-Equal areas travel equal time -This is because the planets move faster when they are close to the Sun

Based on your answer in part (b) and what we know about stars, what color did the CMB radiation originally appear as?

3000 Kelvin M stars appear red because their blackbody emits more red than blue light. The CMB appeared red.

Wavelength

= color -extends far beyond visible light into the EM spectrum X>UV>Vis>Infra>Microwave>Radio in energy -all light the same speed -Intensity/Brightness plotted vs. wavelength is a spectrum >>> information

Matter

=Atoms -the unlike attract, electrons and protons. the like repel! -the nucleus contains most of the atoms mass, with positively charged protons and neutral neutrons -around the nucleus, there is the cloud of moving negatively charged electrons

The new James Webb Space Telescope will be able to readily see galaxies from a time when the universe was 1/8 as big as it is now. The light from an 8000 Kelvin A star in one of these galaxies is highly redshifted so that when JWST sees it, it matches the blackbody of what temperature? (Hint: CMB is currently appears as a 3 K blackbody and came from when the universe was 1000 times smaller.) A) 1000 K B) 8000 K C) 8003 K D) 18000 K E) 64000 K

A) 1000 K

Unlike many other religions, Joseph Smith taught that "the elements are eternal" (D&C 93:33) and that the creation of this Earth was a matter of organizing pre-existing material (see Abraham 3-4). How does this match our modern view of cosmology? A) As the universe expands it is not creating new material, but just spreading out the existing material B) As the universe expands, new "dark energy" turns into "dark matter" C) The Big Bang created only a small fraction of the Helium in the universe today. D) The Earth formed immediately after the Big Bang

A) As the universe expands it is not creating new material, but just spreading out the existing material

In the "Cosmic Calendar" model, the age of the universe is compressed to one year. In this analogy, roughly when did the universe become transparent, allowing photons to stream freely to our microwave telescopes today? A) January 1 B) March 21 C) September 3 D) December 29

A) January 1

Many exoplanets orbiting other stars likely have no tilt between their rotation and revolution. If all else was similar, what would be different on these planes? A) There would be no changing seasons B) There would be no night and day C) The constellations wouldn't change during the year

A) There would be no changing seasons

Describe at least 5 distinct steps in the evolution of a star. You may choose a star of any 3 mass, but specify which mass you choose.

All start 1) from a large cloud of gas and dust that 2) collapses into a protostar when 3) Hydrogen fusion prevents further contracting and places the star on the Main Sequence. Then 4) Hydrogen core burning ends and Hydrogen shell burning begins making the star a Red Giant. At this point, the histories can diverge depending on the star mass; see the Summary slides for a review.

A white dwarf is A) An object in between planets and stars (L, T, or Y spectral type) B) A remnant of a star that is about the size of Earth C) A hot, low mass main sequence star D) A star at the beginning of its life with a temperature way less than the Sun

B) A remnant of a star that is about the size of Earth

BYU just made its annual astronomy patch. What is going on in the top part of the diagram? (Hint: observe carefully how the shape of the yellow circle changes.) A) A supernova is expected to occur on August 21, 2017 B) The diagram is showing the phases of the Moon which will be unusually concentrated around August 21, 2017 C) A total solar eclipse is expected on August 21, 2017 D) In a rare occurrence, the dark side of the Moon will appear on August 21, 2017

C) A total solar eclipse is expected on August 21, 2017

How do space probes to the outer solar system pass through the asteroid belt without being obliterated by collisions? A) They don't - we lose about one in four, but those are acceptable costs. B) The spacecraft send back video footage to Earth, where astronauts carefully pilot them through c) Collisions are not a major threat since asteroids are so far apart that spacecrafts sail safely through

C) Collisions are not a major threat since asteroids are so far apart that spacecraft sail safely through.

Suppose the Universe were not expanding, but were staying the same size (called "steady state"). How should galaxy Doppler shifts be correlated with distance? A) The inferred velocities would be directly proportional to distance B) Larger distances would correlate with stronger blueshifts C) Doppler shifts would be relatively random, some blueshifted and some redshifted. D) Distant galaxies would be even more redshifted than we see them in our universe

C) Doppler shifts would be relatively random, some blueshifted and some redshifted.

What do we call the days of the year when the Sun rises exactly due East and sets exactly due West? A) Solstices B) Circumpolar C) Equinoxes D) Ecliptic days E) Equinoxes

C) Equinoxes

If a star formed from the same cloud as the Sun at the same time, but had half the Sun's mass, what kind of star would it be today? A) White dwarf B) Red giant C) Main sequence star D) Asymptotic Giant Branch (AGB) star

C) Main sequence star

How often does the Moon rotate? (Hint: we discussed in class that it is in this special "locked" state due to tides.) A) Once per day B) A little more than once per day, because you have to account for the motion of the Moon's orbit around the Earth C) Once per month D) Once per year E) The Moon doesn't rotate

C) Once per month

The word "quasar" comes from "quasi-stellar radio source." What makes quasars similar to stars? A) Quasars and stars show similar parallax and/or proper motion B) Quasars and stars have similar Doppler shifts in their spectra C) Quasars and stars are both unresolved to most telescopes D) Quasars and stars both often have binary companions

C) Quasars and stars are both unresolved to most telescopes

Which was the most challenging motion of an object seen in the sky to describe with Ptolemy's geocentric model and how did the model handle it? A) Stars rising and setting; celestial sphere model B) Motion of the planets; planets move in ellipses C) Retrograde motion of the planets; planets moved in circles-on-circles D) Sun's path along the ecliptic; Sun orbited the Moon

C) Retrograde motion of the planets; planets moved in circles-on-circles

Which is an accurate significant difference between how we learn scientific and spiritual truth? A) Learning spiritual truth does not include any experimentation B) Scientific truth comes quickly, but spiritual truth comes line by line C) Scientific truth is objective, but spiritual truth is subjective D) Spiritual progress focuses on self-correction, but science does not

C) Scientific truth is objective, but spiritual truth is subjective

A full moon will be rising on the horizon at A) Changing times of day as the Earth orbits the Sun B) Sunrise C) Sunset D) Midnight E) Noon

C) Sunset

KBO 2017DR123 has 5 stable clones, a typical NepPerRatio of 1.7133-1.7146, and proper elements which imply a Delta V of 420 m/s. Why is 2017DR123 unlikely to be a Haumea family member? A) Haumea family members came from a collision that put objects into unstable orbits B) The KBO is clearly in the 7:4 resonance since 7/4 = 1.75 C) The "dynamical distance" is too large D) The unknown spectrum would not show strong water ice

C) The "dynamical distance" is too large

Why do stars take such a convoluted path on the H- R diagram as they age? A) As they burn Hydrogen in their cores into Helium, they are changing mass, so an A main sequence star will evolve into a K main sequence star B) The star goes back and forth between using nuclear fusion and nuclear fission to generate energy C) The competition between temperature-induced pressure and gravity is changing based on different kinds of fusion D) These paths are mostly theoretical since we don't really observe objects in these parts of the H-R diagram

C) The competition between temperature-induced pressure and gravity is changing based on different kinds of fusion

What is at the center of the Milky Way? A) A massive pulsing neutron star B) A 100-solar mass black hole C) A supermassive black hole shining brightly due to a jet pointed our direction D) A supermassive black hole inferred from orbiting stars E) Temperatures and pressures high enough to fuse Helium leading to a high luminosity

D) A supermassive black hole inferred from orbiting stars

The New Horizons mission was able to measure a precise density for Pluto and Charon: 1.860 g/cc and 1.707 g/cc respectively. What can you conclude from these densities? A) Pluto has a large rocky core, but Charon has no rocky core B) Charon has a large rocky core, but Pluto has no rocky core C) Neither Pluto nor Charon have any rock, since they are beyond the ice line where there is no rock. D) Both Pluto and Charon have significant amounts of both ice and rock

D) Both Pluto and Charon have significant amounts of both ice and rock

In the densest galaxy clusters, there are almost no spiral galaxies. Which is the most likely reason for this? A) Since elliptical galaxies are much older than spirals, there are no young stars left in the disk. B) In clusters, gas is strongly attracted to the space between the galaxies, leaving nothing for star formation. C) Two galaxies in the same general region of space will pull each other into spherical shapes by tides. D) Denser galaxy clusters are more likely to have galactic mergers which will turn spirals into ellipticals.

D) Denser galaxy clusters are more likely to have galactic mergers which will turn spirals into ellipticals.

Arugably, the sidereal day is the more fundamental unit of time, since it is a measure of the true rotation rate of the Earth. Why then do we set our clocks to solar time instead of sidereal time? A) We cannot divide the day into 24 equal hours of sidereal time B) In sidereal time, the Sun wouldn't land perfectly on the meridian every day; it could be off be as much as 15 minutes. C) Different clocks tick at different rates depending on latitude in sidereal time D) We set our clocks with a focus on the Sun's position in the sky, e.g., "noon" is set to when the Sun is highest in the sky.

D) We set our clocks with a focus on the Sun's position in the sky, e.g., "noon" is set to when the Sun is highest in the sky.

Which part of the electromagnetic spectrum has the highest energy photons? A) Radio B) Visible C) Infrared D) X-ray

D) X-ray Recall that the EM spectrum goes: X, UV, Vis, Infrared, Microwave, Radio in order from most energetic (highest frequency, shortest wavelength) to least energetic (lowest frequency, longest wavelength).

At the present day, the CMB looks different. Describe how the photons from the CMB are different now than they were in the past in wavelength, frequency, and energy.

Due to the expansion of the universe, we say that the wavelength of light increased, lowering the frequency and energy of photons. (The CMB now looks like a 3 K blackbody).

Which of the following sequences of the Moon phases will occur one right after the other? A) Third quarter, waxing gibbous, full, waning crescent B) Waxing gibbous, waxing crescent, new, waning crescent C) Waning crescent, first quarter, full, waxing crescent D) Full, waning gibbous, half moon, waning crescent E) New, waxing crescent, first quarter, waxing gibbous

E) New, waxing crescent, first quarter, waxing gibbous

Maxwell's Equations:

If you wiggle an electron up and down, it makes magnetism. Continuing to wiggle it, that magnetism is wiggling as well which makes electricity, and that electricity continues to wiggle. By wiggling an electron, you can create a self-propagating electromagnetic wave. Maxwell used his equations to show that the speed of that wave was the speed of light.

Luckily, Kepler has shown that STIPs are equally as common around stars with a wide range of metallicities, so most stars should have planets. However, why do we not expect planets around the very first population of stars after the Big Bang? (1 sentence)

Immediately after the Big Bang, there are no metals, only Hydrogen and Helium. Here we mean "metals" for a stellar astronomer, which, for a planetary scientist, would consist of "ices", "rocks", and "iron/metals". If there is no ice, rock, or metals, then there is nothing for planets to be made from. (Even gas giant planets require a solid core to initiate gravitational accumulation of H/He gas.)

Briefly describe the Cosmic Microwave Background (CMB) including at both what it looks like observationally and why we think it looks the way it does. (3 sentences)

See the summary slides. Observationally: homogenous, isotropic, perfect 3K blackbody with tiny modulations. This is what is expected from when the universe was hot and transitioned from opaque to transparent: the photons from this event travel freely through space until reaching us. It is homogenous and isotropic because the entire universe was glowing.

There is a potential problem in extrapolating our results to the whole universe. Kepler only surveyed stars in the galactic disk. How does the metallicity (prevalence of "metals" as defined by stellar astronomers) of stars in our galactic disk compare to stars in common elliptical galaxies? (1 sentence) (Hint: there is a correlation between metals and age.)

The Big Bang created no metals, so as stars fuse H/He into metals, the fraction of metals in the universe is increasing significantly. Younger stars reap the gas and dust expelled by older stars and thus age is correlated with metallicity. The MW disk is young and metal-rich and elliptical galaxies are old and metal-poor.

(c) How do the seasons on Mars compare to the seasons on Earth? Why? A rough qualitative explanation is all that is expected. (2 sentences)

They are very similar. Since axis tilt controls the strength of the seasons and the axis tilts are almost identical, the strength of the seasons are basically the same. However, since Mars takes longer to orbit, the seasons are longer. [For this question, either one of these facts would have received full points.] Note that the length of the Martian day and the size of Mars are not relevant.

Newton revolutionized physics:

velocity: speed and direction acceleration: change in velocity momentum: mass*velocity momentum: how hard it is to stop something forces: push/pull that accelerates or changes momentum angular momentum: mass*velocity*size mass: how much stuff there is weight: the force of gravity on mass volume: how much space does something take density: mass/volume, how tightly packed

Exoplanets and Life

-Exoplanet = planet around another star, now a major subfield of astronomy -Because they are very close to a very bright star, planets are difficult to detect by taking a picture. Instead, we use indirect methods caused by the planet's gravitational pull on the star (just like for binary stars) + Radial Velocity method measures mass + Transit (=eclipse) method measures size + Combination of mass and radius give density composition, very valuable -Kepler Space Telescope found thousands of transiting planets, including hundreds in systems of planets: extremely valuable for understanding planetary systems -Exoplanets are different from solar system planets: + Hot Jupiters: Jupiter-like planets orbiting 100 times closer than Jupiter + STIPs: systems of 5-7 planets a little larger than Earth crammed into a region smaller than Mercury's orbit; very common + Planets like Earth not yet detectable, but planets just like our Jupiter have been seen -Habitable Zone: region around a star where a planet would have liquid water + Potentially Habitable Planet (PHP): Earth-sized planet (solid surface) in the HZ (liquid water), two of the basic criteria thought to be important for life -STIPs are common in the HZ around M stars M stars have ~1 PHP each -Universe is filled with M stars and thus ~1021 Potentially Habitable Planets!

Chapter 25 - Milky Way

-Faint concentration of light in a particular region of the sky is explained by being in a disk of stars + But dust, which darkens and reddens visible light, makes it even harder to figure out where we are + Galaxy is 100,000 light-years across and we are half way between center and age -Galaxy has 3 components: 1) Disk: flat orbits and shape, gas/dust > active star formation > bright/young stars 2) Central bulge/nucleus: small, spherical orbits and shape, old 3) Halo: large, spherical orbits and shape, old and low metallicity stars -Center of galaxy contains dark supermassive black hole -Observing stars orbit too fast beyond the edge of the disk shows that the Galaxy contains 90% dark matter in a halo ~3x as large as the disk -MW has eaten other galaxies and is headed for Andromeda nearby

Newton's Third Law of Motion

-For every force, there is always an equal and opposite reaction force

Chapter 19 - Astronomical Distances

-In the solar system, we can measure distances using radar and light-travel time -We use parallax to measure distances to nearby stars: observing from the Earth 6 months apart changing the position of nearby stars relative to distant stars by an angle p. -When p is in arcseconds and d is in "parsecs", then d = 1/p: smaller angles mean farther distances -Standard candles are used to find distance by comparing luminosity to apparent brightness -The periods of Cepheid variable stars are directly related to their luminosity: standard candle that measures distnaces too far for parallax, reaching even nearby galaxies -Despite the H-R diagram, stars are not great standard candles because red stars can be dwarfs, giants, or supergiants

Chapter 11: Jovian Planets

-Jovian planets separated into gas giants (Jupiter and Saturn) and ice giants (Uranus and Neptune) + All have ~10 Earth mass icy/rocky/metal cores + All have rapidly rotating atmospheres, storms + All have no solid surface, rings, and many moons + All were visited by spacecraft flybys ++ Jupiter/Saturn got orbiters -Jupiter/Saturn internal pressure creates metallic hydrogen > strong magnetic fields -Internal heat escapes through convection, causing weather, that is stretched out into latitudinal bands by the rapid rotation -Clouds create color by freezing minor constituents; different colors > different chemicals < different temperatures

Chapter 23 - Stellar Remnants

-Low mass stars form white dwarfs which are supported by electron degeneracy pressure + Mass of Sun, size of Earth + If mass is added (by accreting from a binary companion), then the white dwarf can exceed the 1.4 solar mass Chandrasekhar limit > Type Ia Supernova -Medium-mass stars undergo Type II supernova and create neutron stars (basically giant nuclei) + 2 Solar masses, size of city + Magnetic fields and rapid rotation can lead to pulses of light > pulsars -High-mass stars undergo Type II supernova, but the remnant is too massive even for neutrons > black hole

Chapter 16: Solar Interior

-Many different forms of energy: heat, light, gravity, motion, chemical bonds, ..., and mass + E=mc2 means that a tiny mass produces a huge amount of energy; only this can power the Sun -Nuclear reactions convert mass to energy: fusion (combining nuclei lighter than iron) and fission (splitting nuclei heavier than iron) -Sun uses fusion of Hydrogen nuclei (= protons) at center; to overcome electric repulsion and get the protons close enough for the strong nuclear force requires 10,000,000 K temperatures and intense pressure -Pressure is how hard a gas pushes outward; in Sun (and other bodies), force of pressure balances crushing force of gravity -Solar interior models can explain Sun well, including "helioseismology" and detection of shy neutrinos (new kind of particle that illustrates connection between particle physics and astrophysics)

Chapter 24 - Black Holes

-Mass is so concentrated, nothing can stop them from collapsing into a single point called "singularity" -Density is so high that even light cannot move fast enough to escape > event horizon (a few km) + Black holes are detected by their gravitational influence on other objects, including "accretion disks" which often emit very high energy light -Gravity so intense, must use Einstein's General Theory of Relativity > mass "curves" space-time + Also gives gravitational lensing since light travels through curved space-time -Supermassive black holes are found at the centers of galaxies

Chapter 14: Meteors

-Meteors are pea-size asteroids that burn up in the upper atmosphere producing a streak incorrectly called a shooting/falling star; sometimes comes in "showers" -Meteorites are larger asteroids that make it to the surface of the Earth and teach us much about the solar system, e.g., radioactive dating age = 4.5 billion years -Meteorites have three compositions: stony, stony-iron, irons; last two come from core (and near core) of a now-destroyed differentiated protoplanet -Some meteorites are "primitive": scoops of the solar nebula unaltered by heat or pressure or water

Chapter 12.4 (Pluto) and 13 (Small Bodies)

-Now that we know that Pluto is tiny and shiny (instead of big and unreflective) and part of a larger population of KBOs, it is now classified with a new group of dwarf planets, even though it has 5 moons and a thin atmosphere -Incredible New Horizons mission shows active geology on this tiny world, e.g., convection in Nitrogen ice glaciers -Asteroids are small: Ceres, the largest, is only 1000 km across; as you go smaller, there are more and more asteroids collisions as manifested in impact craters and collisional families (asteroids with similar orbits because they are collisional shards) -Because they are small, they are cold and their gravity is too weak to reshape them into spheres; gravity is weird on their surfaces -Most asteroids orbit between Mars and Jupiter on moderately eccentric and inclined orbits, but many orbit near Earth, which is important for impacts, science, and mining -Comets have a "dirty snowball" nucleus that starts to evaporate near the Sun, forming an atmosphere that escapes due to small gravity and becomes (multiple) tails -Comets have two types of very eccentric orbits: "short-period" comets come from the Kuiper Belt, "long-period" comets come from the Oort cloud, a 100,000 structure -Orbits of large icy KBOs show that Neptune has moved. Present-day gravitational interacts cause orbits of KBOs to change, including large changes in the case of resonances which happen when there is a repeating pattern in their orbits due to a ratio of periods that is similar to ratio of small integers). Lab is to study orbits of potential Haumea family members.

Chapter 18 - Understanding Stars

-Observational/Selection Bias means that stars we see in the sky are not representative of what's really out there -Binary stars: both orbit the center of mass, causing detectable Doppler shifts that we use to measure masses -Eclipsing binaries: stars eclipse each other causing detectable brightness dips that we use to measure radii -Combining information on stars and plotting Luminosity vs. Color/Temperature gives an "H-R Diagram". (Temperature increases to the left.) This shows that 90% of stars fall on "the main sequence" where stars are fusing H to He + Stars are very simple, everything about them is determined by their mass + Size increases from lower left to upper right (because L=R2T4) -O stars are hotter, more massive, larger, more luminous, rarer, and have shorter lifetimes than M stars.

How does science work?

-Observations/Experiments: Always follow the data -Goal: Predict the future -It's objective -It's self-correcting: rigor, skepticism, data-centered

Kepler's Third Law

-P^2=a^3 (only if P is in years and a is in AU) -P is orbital period, the time the time it takes for a planet to make a complete revolution around the Sun -P increases with semi major axis -updated by Newton, P^2 x (M1 + M2) = a^3

Chapter 8: Earth

-Pressure = weight of material above you -Seismic waves reveal layered interior: solid iron inner core, liquid iron outer core, "solid" rocky mantle, brittle rocky crust -Convection(=boiling) important in atmosphere (weather), mantle (plate tectonics), and core (moving metals magnetosphere) -All rocks on Earth have been processed by heat (igneous volcanoes), erosion (sedimentary), and/or pressure (metamorphic) -Floating plates pull, subduct, push, and slide, leading to earthquakes, volcanoes, and mountains -Earth atmosphere is layered: highest pressure bottom layer experiences weather; climate is the long-term average of weather + Oxygen in atmosphere was created by life -Certain gases (CO2, H2O) have infrared spectral lines that redirect light from Earth surface blackbody. These greenhouse gases retain heat like a blanket causing global warming. Human activity has produced unprecedented levels of atmospheric CO2 causing warmer temperatures, with long-term ecological damage hard to predict or control. -Impacts by asteroids have caused mass extinctions, but these are extremely rare; no current global risk, though minor local risks remain.

Chapter 12: Large Moons

-Regular moons form in circumplanetary "subnebula" like solar system + Gallilean satellites of Jupiter even have "ice line": rocky Io inside + Many irregular moons on crazy orbits: captured asteroids/comets -Jupiter's moons affected by tides, much stronger closer in Io: intense tidal heating > volcano world Europa: some tidal heating > subsurface liquid ocean (and life?) Ganymede: a little tidal heating > tectonics Callisto: cold, water ice is hard as rock, craters -Saturn's Titan is the only moon with 1) an atmosphere, 2) liquid (methane) on its surface lakes and rivers + Water ice forms the "rocks" and sand dunes -Saturn's Enceladus is a tiny moon tidally heated to have a subsurface liquid ocean that is expelled into geysers -All jovian planets have rings; Saturn's are the best + Boulder-size ice particles that are only ridiculously thin orbits + Cannot coalescence into moons because tides rip them apart

Chapter 7: Solar System

-Solar System planets can be divided into rocky small terrestrial planets (Mercury, Venus, Earth, and Mars) and gaseous/icy large jovian planets (Jupiter, Saturn, Uranus, Neptune)+ Jovian planets also have rings and many moons -Planets are much more massive, more circular, and have orbits less tilted (inclined) than small bodies: dwarf planets, asteroids, comets, Kuiper Belt Objects (KBOs) -Surface temperatures (50-500 K) are determined by proximity to the Sun and atmosphere -Internal temperatures are determined by slow cool down so that the center is hottest + Planets were originally hot enough to be molten > differentiation = dense materials > center -Internal heat lost fastest for small bodies + Internal heat powers geologic processes like volcanism and tectonics + Smaller than ~Earth > now geologically "dead" -Surfaces can be dated through impacts (more = older) or radioactive dating (half of the isotopes change/decay every half-life) -Planet Formation Hypothesis: large cloud of gas and dust collapses under gravity; conservation of angular momentum causes this solar nebula to spin rapidly, leading to a disk shape with everything orbiting the same direction. Dust accretes into planetesimals; planetesimals accrete into planets. Only solid material participates in accretion, so beyond the "ice line" abundant ices participate, allowing jovian planets to grow larger, faster. Jupiter/Saturn reach a gravitational size to start runaway accretion of solar nebula gas.

Chapter 22 - Stellar Evolution

-Stars resist gravitational collapse through pressure < temperature < energy < fusion -When Main Sequence (MS) stars run out of H in the core (where T high enough for fusion), they can't resist collapse and start to change size + Stars are on the MS only during initial H fusion + But collapse brings fresh H to region outside the core, which boosts fusion and pressure > increased size > giant star (leaving the MS) -Continued collapse can reach T high enough for Helium to fuse to higher elements, depends on mass -Low mass stars (<4 solar masses) go from Red Giant Branch (H shell) to other branches (He fusion), but never fuse past Carbon/Oxygen + Planetary Nebula and White Dwarf, which is held up by electron degeneracy pressure if it is smaller than the Chandrasekhar limit of 1.4 solar masses -High mass stars (>8 solar masses) go through similar stages, but can reach the super high pressures/temperatures needed to fuse Carbon and Oxygen into higher elements, until they reach Iron, which has no extra energy + Core collapse (Type II) supernova which forms all elements + Protons combined with electrons to leave neutron star or black hole

Summary of Chapter 6

-Telescopes gather (or "focus") light into a single place using lenses (to bend/refract) or mirrors (to reflect) -Bigger telescopes gather more light and have a better angular resolution (= can see finer details). -The angular resolution is limited by the wave nature of light and means that basically no astronomical object is "resolved" so we cannot measure how big things -Atmosphere blurs images; light pollution makes it harder to see faint objects; blocks certain wavelengths of light completely space telescopes: expensive but valuable -Images are recorded with CCDs (like digital cameras) that are divided into colorblind pixels ~all astronomical images are highly processed in terms of color and brightness -We use telescopes for imaging (pictures), spectroscopy (spectra), and time monitoring (brightness variations over time)

Geocentric Universe

-The belief that we are the center of the universe -Ptolemy -Kepler overturned the geocentric model, using Brahe's observations, and developed three laws of planetary motion

Wein's Law

-The peak wavelength is the color of the maximum intensity/brightness of light. -Spectrum is a wavelength! landa=(3x10^6)/T -T is temperature in K. -landa gets smaller with increasing T because T means faster moving atoms, which means higher energy/frequency wiggles, which means higher energy photons

Heliocentric Universe

-The sun being the center of the universe -First proposed by Copernicus -Galileo further proved it. Observed phases of Venus only possible in a Heliocentric model WITH HIS TELESCOPE -Kepler and Brahe further showed this.

Chapter 20 and 21 - Star Formation

-There is gas and dust between the stars; large clouds can collapse to form clusters of stars when they get cold enough -More massive stars form, life, and die fastest + Looking at the main sequence of a star cluster, you can see which stars have died age -Sun will last ~10 billion years, O stars ~10 million, M stars ~10 trillion

Chapter 10: Venus and Mars

-Venus is ~same size as Earth, recent geological activity (volcanism) -Hard to study since surface is so hot + Runaway greenhouse made thick CO2 atmosphere that retains heat -Mars has two surfaces: cratered highlands and smooth lowlands -Mars robotic missions focus on water on present/past Mars + Many geological (river channels) and chemical evidences for past water on waters; possibly subsurface present water... and life??

Phases of the moon

-Waxing: gets fuller -Waning: gets less full -Solar eclipse is when the moon covers the sun -Lunar eclipse is when the earth covers the moon

Stefan-Boltzmann Law for Blackbodies

-hotter blackbodies are brighter at all wavelengths L=R^2T^4 -L is luminosity = the total energy output in W -R is radius = size m -T is temperature K

Light

-is a self propagating electromagnetic wave composed of particles (photons) each with their own frequency, wavelength, and energy -frequency is inversely proportional to wavelength and directly proportional to energy -red=long wavelength, low frequency/energy -blue=short wavelength, high frequency -it travels in a straight line in all directions, with intensity/brightness getting weaker with the inverse square of distance

Declination

-latitude

Right Ascension

-longitude

Brahe

-obtained precise observations of planets

Kepler's First Law

-orbits are eclipsed with the Sun at one focus -Ellipse size is determined by semi major axis a -Ellipse shape is determined by eccentricity e -Earth's eccentricity is presently 0.016

Why are there seasons?

1) Separation of timescales -Daily motion: ignore the yearly motion, the sun is fixed like a star, Sun rises in the east and sets in the West just like everything else -Yearly motion: ignore the daily motion and only worry about the Sun at noon. 2) Separation of rotation and revolution -The Earth's rotation axis is fixed while it goes around the sun -Revolution is when an object turns around an object. 3) Hemisphere perspective -half the earth in daylight, half in darkness 4) Sunlight angle directness -more direct sunlight spreads out energy less. AXIS TILT is the origin of the longer days and more direct sunlight in the summer. Without it, we would not have seasons.

Newton's Universal Law of Gravitation

1. Every mass attracts (exerts a force) every other mass 2. The force is directly proportional to the product of their masses 3. The force is inversely proportional to the square of the distance between them F=Gx M1M2 / d^2 M1 and M2 are in units of the mass of the Sun -This explains the WHY of Kepler's laws -This also shows that planets in the solar system subtly change each other's orbits: discovery of Neptune

Planet Y's orbits Star A with a semimajor axis of 1 AU and Planet Z's also orbits Star A with a semimajor axis is 2 AU. Planet Z is 6 times as massive as Planet Y. Which of the following correctly describes why the gravitational force between Star A and Planet Z is larger than the force between Star A and Planet Y, even though Planet Z is further away? A) From 𝐹 = 𝑚𝑎, since the mass and semimajor axis (a) are both larger for Z, the force will be larger. B) From 𝐹 = 𝐺𝑀1𝑀2 , even though Z is twice as far away, this has the effect of 𝑑2 reducing the force by a factor of 4. But this is more than compensated for by Planet Z's higher mass. C) From 𝑎3 = (𝑀1 + 𝑀2) × 𝑃2, Planet Z will have a much larger period than Planet Y which is only possible if the force is also larger.

B) From 𝑭 = 𝑮𝑴𝟏𝑴𝟐 , even though Z is twice as far away, this has the effect of 𝒅𝟐 reducing the force by a factor of 4. But this is more than compensated for by Planet Z's higher mass. Don't let the equations and math scare you. This problem is only about identifying the correct equation: since the problem is talking about gravitational force and B is Newton's Universal Law of Gravitation, it must be correct. In F = ma, the a stands for acceleration NOT semimajor axis, so that can't be right. (C) proposes that period and force are somehow connected, which they are not. The explanation is B also makes sense: doubling the distance reduces the force by a factor of 4, since it is an inverse square law. But since Planet Z is 6 times as massive as planet Y, and 6>4, the force will be bigger. [Why, if the gravitational force is bigger, does Planet Z orbit more slowly? We didn't discuss this in class, but the force isn't what matters... it's the acceleration. Though the force on Z is stronger, Z is also harder to move/accelerate because it is more massive (F = ma). In this way the mass of the planet "cancels out" and orbits are primarily controlled by the mass of the Sun.]

A student incorrectly draws the orbit of an elliptical comet (blue) on a diagram showing the Sun (yellow) and the four giant planets (red). Which law is this orbit violating? (Hint: foci) A) Conservation of Momentum B) Kepler's First Law C) Kepler's Second Law D) Kepler's Third Law

B) Kepler's First Law

A tenuous cloud of gas in the laboratory is observed by two spectrometers looking at it from different directions. The first detects emission lines and the second detects absorption lines. How can this best be explained? A) The first observer sees the gas in front of a hot background B) The second observer see the gas in front of a hot background C) The radial velocity of the gas is different for the two spectrometers D) The atoms in the gas are forming molecules

B) The second observer see the gas in front of a hot background

A recent extensive study of undergraduates showed that doing a combination of three things would increase your likelihood to thrive after college by an incredible factor of 10. Which of the following is NOT one of these important pieces of advice? A) Find a mentor who encourages you towards your (realistic) dreams B) Work extra hard to get a GPA above a 3.9 C) Find professors that make you excited about learning and care for you as a person D) Get a long-term internship/research job

B) Work extra hard to get a GPA above a 3.9

You observe two stars at the same distance that is nearby on a galactic scale. One is in the disk of the Milky Way, the other in a direction perpendicularly out of the disk. (Hint: draw a diagram.) Chances are that the disk star will be A) less luminous, have a smaller Doppler shift, and a lower metallicity. B) more luminous, have a smaller Doppler shift, and a higher metallicity. C) less luminous, have a larger Doppler shift, and a higher metallicity. D) more luminous, have a larger Doppler shift, and a lower metallicity.

B) more luminous, have a smaller Doppler shift, and a higher metallicity.

n the "Cosmic Calendar" model, the age of the universe is compressed to one year. In this analogy the Earth formed in September. What is the age of the Earth? A) 5 million years B) 5 million light-years C) 5 billion years D) 5 billion light-years E) 5 trillion years F) 5 trillion light-years

C) 5 billion years You have to remember that the age of the universe (1 "Cosmic Calendar" year) is 14 billion years. Then, roughly, each month corresponds to 1 billion years and September (5 months before now) is about 5 billion years ago. Light-years is a measure of distance, not time.

At the North pole, the Sun is occasionally a circumpolar "star" because of its declination. Some students are discussing whether the Moon could be circumpolar at the North Pole. Which statement is INCORRECT? A) Student 1: Sometimes the Moon covers the Sun in a solar eclipse... B) Student 1: ...so if the Sun is circumpolar then the Moon could also be, since they are in the same place in the celestial sphere. C) Student 2: But the Sun becomes circumpolar because it changes it declination, getting closer to the North Celestial Pole; we didn't discuss in class whether the Moon did the same thing. D) Student 1: But I remember that there's a total solar eclipse coming up in August; that is before the Autumnal Equinox, so the Sun and the Moon must both be at Northern declinations (above the celestial equator). E) Student 2: Just because its hot in the Northern hemisphere in August doesn't mean its summer everywhere. It's winter in the Southern hemisphere, so the Sun and Moon wouldn't be circumpolar, even at the North Pole.

E) Student 2: Just because its hot in the Northern hemisphere in August doesn't mean its summer everywhere. It's winter in the Southern hemisphere, so the Sun and Moon wouldn't be circumpolar, even at the North Pole. During a solar eclipse, the Moon and Sun are at the same location, including declination, which controls whether an object is circumpolar. The Sun's declination does change, but it is still North in August, which means that it is still circumpolar in August at the North Pole. While Student 2 is correct that it's winter in the Southern hemisphere, that doesn't change the fact that the Sun is at Northern declinations at that time. (In fact, that is WHY it is winter in the Southern hemisphere; the Sun's northern position means less daylight and less direct sunlight.) 12 It turns out that the Moon has a wide variety of declinations due to its tilted orbit around the Earth and gravitational twisting of the Moon's orbit by the Sun.

(c) Now give an example from our solar system of an object with endogenous geological activity that is powered by external forces and would otherwise be geologically dead.

External gravitational forces can cause tides which heat up the interiors of planets and can maintain geological activity on small moons. The primary examples are Io and Enceladus,

Newton's Second Law of Motion

F=ma -forces accelerate, but more massive objects are harder to

Gravity is a critical concept for understanding the universe, even though it is relatively weak. 2 (a) Name one of the four fundamental forces that is stronger than gravity (b) Describe qualitatively Newton's Universal Law of Gravitation (c) Give an example of how astrophysicists have learned something new about the solar system thanks to our understanding of gravity. (1 sentence) (d) Give an example of how astrophysicists have learned something new about the Galaxy thanks to our understanding of gravity. (1 sentence)

Gravity is one of the four fundamental forces, but is the weakest of them all so any of electromagnetism, strong nuclear force, or weak nuclear force would be correct. The Force between two objects is proportional to their massives and inversely proportion to (the square of) the distance between them. Many examples are possible including the discovery of Neptune, the measurement of the mass of Pluto (or many other things), resonances, etc. Several examples are possible, but most prominent are the characterization of a supermassive black hole at the center of the Galaxy and the massive dark matter halo of the Galaxy.

The CMB shows very slight fluctuations. Explain how these small fluctuations eventually grow into large scale structure. Include the concept of a positive feedback loop in your explanation. (2 sentences)

Large scale structure emerges from slight variations because gravity amplifies these effects. If one area of the universe is slightly denser, then it will have a slightly stronger gravitational pull, which will add more mass to that region make it even more dense. This positive feedback loop is continuing today as gravity is concentrating material along filaments.

How do we measure the distance to the Andromeda Galaxy? (Hint: we can see individual stars in Andromeda.) (1 sentence)

M31 is too far for parallax but too close to use Hubble's Law. However, we can detect individual Cepheid variable stars and use them as standard candles to infer from the apparent magnitude of the stars/galaxies that they are very far away.

(c) Give a specific example of the effect of solar activity or space weather on planets in the solar system (including Earth). (1 sentence)

Many examples are possible: aurorae (Northern/Southern lights) on the Earth (and other planets!), changing the size and shape of planetary magnetospheres, messing with orbiting satellites, the electrical grid, and other issues on Earth, etc.

(a) Give an example of something in astronomy that cannot be meaningfully drawn to scale. Include an explanation of why it can't be drawn to scale. (1-2 sentences)

Many examples are possible: the reason why is that the objects being drawn have sizes that are so different (a factor of 105 = 100,000) that either the paper you have to draw on is miles across or the objects have to be drawn so small that they can't be seen. For example, drawing the solar system to scale on this piece of paper would require drawing the planets as dots far too small to see.

We relied on Kepler's discovery of the prevalence of "Systems with Tightly-spaced Inner Planets" which showed lots of planets with periods near 10 days. How do we know that an orbital period of 10 days corresponds to planets that are much closer to their star than the Earth is to the Sun? Describe qualitatively. (2 sentences)

Newton's Version of Kepler's Third Law (and arguments about the strength of gravity) show that shorter orbital periods happen at smaller semi-major axes. This is counteracted a bit by the lower mass of M stars, but this is not a dominant effect (because a is cubed and P is square in NVK3L and because the mass is only ~1/10th while the Period is ~1/30th). [I should have added a caveat to this problem to ignore the difference in stellar mass.]

(d) Does stellar activity affect volcanism on the Earth? Why or why not? (1-2 sentences

No, volcanism is powered by the interior heat of the Earth which is unaffected by the Sun.

(a) What is the cause of "solar activity" on the Sun? Include one reason why we think this is the cause of solar activity. (2 sentences)

Solar activity is caused by twisting magnetic fields. We see the effect of magnetic fields on the spectra of sunspots and we see how charged particles (normally curtailed by magnetic fields) stream freely after the magnetic fields change. Etc.

(b) How does solar activity change with time? (1 sentence)

Solar activity is cyclical with maxima and minima every 11ish years. [Just cyclical would get full points, you don't have to remember 11 years.]

Space travel?

Space is close but fast. The necessary fuel to get materials into space grows exponentially with mass. -Planetary missions from easiest to hardest: flyby, orbiter, lander, sample return, humans

List the stellar spectral types in order from high-mass to low-mass stars. Give four or more 1 distinct characteristics that are different between high-mass and low-mass stars. Indicate which group is more common in elliptical galaxies.

Spectral types: OBAFGKM O stars are more massive, larger, hotter, more luminous, bluer, rarer, and have shorter lifetimes than M stars. Old elliptical galaxies have no short-lived O stars, but are filled with M stars.

Sun's path across the sky

Summer solstice: Sun is highest in the sky Winter: Sun is lowest in the sky Equinoxes: in the east and sets in the west, exactly -Summer: longest days -Winter: shortest days -Equinox: 12 hour day and 12 hour night

The Stefan-Boltzmann Law says that Luminosity is equal to radius squared times temperature to the fourth power. Which of these stars is most luminous? (You do not need a calculator; qualitative reasoning will give the right answer.)

We want a star that is big and hot. The biggest is F and the hottest is D, so it only remains to decide which of these two is most luminous. Since temperature is a much stronger effect, the slightly smaller but much hotter D wins.