Part 1, Part 2, Part 3- post test 1, Part 4

Particles in Universe:quarks and atoms (structure)

Quarks: up and down quarks combine to form protons and neutrons. Around these there are electrons which forms atoms. Atomic Structure: - An atom consists of an atomic nucleus (protons and neutrons) and a cloud of electrons surrounding it. - Almost all of the mass is contained in the nucleus, while almost all of the space is occupied by the electron cloud. · Electrons do chemistry as they fill up the valence shells to make a stable atom.

Astronomy scale

Quarks> Atoms > Planet > Star > Solar System > Solar Interstellar Neighbourhood > Milky way Galaxy > Local Galactic Group > Virgo Supercluster > Local Superclusters > Observable Universe

Hubble's constant: Kilometres/second/megaparsec

- Hubble's Constant units: Kilometres / second / megaparsec ○ Current best value: 66.93 ± 0.62 km/s/Mpc - From CMB+other data, not a direct measurement [Planck] ○ Direct measurement: 73.00 ± 1.75 km/s/Mpc - A galaxy 100 megaparsecs away: Moving at 6,730 km/s. - A galaxy 1000 megaparsecs away: Moving at 67,300 km/s ○ 26% of the speed of light

Planetary Nebula

- Nothing to do with planets S-process nucleosynthesis Don't need to know this process

EM wave

- Treat light as an electromagnetic wave, electric field and magnetic field that oscillate at right angles to each other

What Bad luck

- "Spiral nebulae" avoided the plane of the Milky Way ○ Zone of avoidance ○ Looks like they are connected with our galaxy ○ Now know that the Milky Way is opaque (due to gas and dust), this is the reason for zone of avoidance, meaning there are spiral galaxies in plane of milky we just can see them - Adriaan van Maanen (1916) claimed to see rotation in M101 ○ If it is as big as the Milky Way, stars move faster than light ○ Now know: it is rotating, but not fast enough for him to see it ○ Optical distortion between two images

Novae and Supernovae

- "Temporary stars" or Novae (singular: nova) ○ Commonly observed in the Milky Way ○ No supernova in Milky Way observed since 1600s ○ Gas accreting in a thin layer on a white dwarf ○ "Burns" via "normal" nuclear fusion - Supernovae can also be caused by accretion on white dwarf - But white dwarf collapses to a neutron star (kaboom)

Thermal history of the universe

- 10-6 seconds after big bang: quark-hadron phase transition (temperature cool so goes from quarks to protons, neutrons) ○ Around 10 Trillion Kelvins ○ Protons and neutrons made out of quarks ○ Protons and neutrons "melt" above this temperature - Universe contains hydrogen nuclei (protons), free neutrons, electrons and positions (anti-electrons) ○ Plus neutrinos, photons and dark matter ○ Nuclei are not stable, so no helium (2 H

Galaxies: Where we are now

- 100 thousand light years in diameter (disk) - Milky Way contains between 1011 and 5x1011 stars (??) ○ Lots of very small, faint stars (which are hard to count) hence the variability

Cosmic Pie (universe)- 13.8 billion years

- 70% dark energy, 25% dark matter, 4% gas and dust, 1% stars - This picture changes as a function of time ○ Dark energy has a constant density ○ Regular Matter density drops by a factor eight each time the universe doubles in size - Ten billion years ago, just a few % dark energy ○ Ten billion years from now, just a few % normal matter ○On our way for universe to be dark energy dominated

The active Earth

- 70% of Earth's surface is covered by water. Mountains are relatively rapidly eroded away by the forces of water.

Red giants and binaries

- 75% of stars have at least 1 companion - First two observed supernova progenitors were in binaries - Can loss some mass onto companion The evolution of one star in binary system can affect the evolution of the companion star

Hubble's "constant"

- A little piece of a curve always looks straight - Does the expansion rate change with time? ○ If so, distant parts of the universe expand at a different (faster) speed... ○ If we have a universe with only standard matter (stars, galaxies) § Expansion slows down Deceleration of expansion of universe - The slope of the line gives Hubble's constant ○ The shape of the line tells us how the "constant" changes ○ We can find acceleration without the distance ladder - We can't see individual stars in the distant universe ○ And galaxies come in sizes ○ But what if we had a star as bright as a galaxy ( we can find its distance from its supernovae)

Parallax equations (PARallax arcSECond )

- A parsec is the distance at which 1 AU subtends an angle of 1 arcsecond - p=d/D where d is the Earth-Sun distance, D is the Sun-star distance, and p is the parallax angle

Thermal equilibrium

- A positron is an electron's antiparticle ○ A positron and electron can annihilate with each other ○ Total charge is zero ○ Electron + positron -> two photons (gamma-rays) - Two gamma rays can convert into a particle-antiparticle pair ○ If they have enough energy: "equilibrium" ○ As the universe cools, energy of photons drops ○Eventually process goes one way

Solar wind and impact on Earth

- A prominence can erupt can 'snap' and then reconnect, but this can send a pulse of solar wind particles towards earth - Solar wind from sun gets deflected by earth's magnetic field and gets deflected away from earth so that is doesn't impact surface of the earth o What we see at the poles of the earth, some of the particles strike atmosphere of earth= produce aurora

The hot big bang (2)

- After a few minutes ○ Have protons, helium nuclei, electrons, neutrinos, photons - But can't (yet) make atoms ○ Photons so energetic they will ionize atoms they hit ○ Universe has to cool before atoms form ○ And a gas of protons and electrons is a plasma ○Light cannot travel through a plasma (like the centre of a star)

Planetary orbits

- All planets in almost circular (elliptical) orbits, orbit around the sun in approximately the same plane. - Sense of revolution: counter-clockwise - Sense of rotation is the same for all planets. All go counter-clockwise ( except Venus, uranus and pluto which goes clockwise). - Orbits generally inclined by no more than 3.4 degrees (except Mercury 7 degrees, and Pluto 17.2 degrees).

Spectral lines & Atomic Transitions

- An electron in an atom can be kicked into a higher orbit when it absorbs a photon with exactly the right energy. - The photon is absorbed, and the electron is in an excited state. (move to higher orbit) - All other photons pass by the atom unabsorbed. - But then an excited electron in an atom can drop to its ground state by emitting photon. - Both processes work at only very narrow specific wavelengths.

Andromeda, 1885

- Andromeda is a spiral galaxy, bigger than the Milky Way ○ A supernova occurred in Andromeda in 1885 ○ Easily visible in a small telescope - Argument went: ○ We see exploding stars. They are quite bright. ○ If Andromeda was a "galaxy" this star would have to be really bright as billions of stars ○ That would be much brighter than the exploding stars we see, therefore it must be close by - Wrong because: it was a supernova, not just a regular nova.

Recombination

- Around 380,000 years after the Bang Bang ○ Universe cooled enough for hydrogen atoms to be stable ○ Universe now transparent ○ Called "recombination", really just "combination" - Microwave background photons can now move freely ○ Provides us with a "baby photo" of the universe

The Cosmological Principle

- Assume the universe is homogeneous and isotropic ○ "Cosmological principle" ○ Isotropic: same in every direction ○ Homogeneous: same in every place - True on average; universe is not exactly the same everywhere

Power Source: Nuclear fusion (what is the energy of the sun?)

- At low temperature: with 2 charged particles are moving slowly, when they get close they will repel (like charged particles repel) - The sun is at high temperature: two charged particles at high speeds in high temperature and when they are close enough, their electric field in unable to repel them and when they fuse and energy is released

The Stable Sun:

- At the core of the sun, fusion reactions are occurring which produces lots of energy and radiates out of sun - This energy (from core of sun) heats balls of gas of the sun which becomes plasma (flows outwards), is constantly fighting against the inward pool of gravity (in equilibrium as a stable object

Tycho Brahe (1546 - 1601 C.E.)

- Best observations pre-telescope, location of planets to a few arc minutes. 10 times better than anything previous. - World model mathematically equivalent to Copernicus' but Sun goes around Earth, all other planets go around the Sun. Stars are 700 times farther away from Saturn than Saturn is from the Sun. (But it is actually 28500 times further).

Cepheid Variables

- Big pulsating stars ○ Two kinds of Cepheid: Population 1 and Population 2 ○ Different period-luminosity relationship ○ So Hubble was out by a factor of a few... - Key step in the Cosmic Distance Ladder ○ Need to know distance to local Cepheids ○ Recent (last decade) measures via parallax

Progress in Astronomy: Technology

- Biggest telescopes - Better detectors - More wavelengths (radio, ultraviolet, microwave) -Computing and data-processing

The doppler effect.

- Blue shift (to higher frequencies) Red shift (to lower frequencies) The light of a moving source is blue/red shifted by: (change in wavelength due to doppler effect)/(actual wavelength emitted by the source) = (radial velocity)/(speed of light in vacuum)] If something is movement, frequencies will change Light moving from blue (loud) to red shifted (away from you quieter)

After Andromeda (discovery of cepheids)

- Cepheid discovered 1923, published 1925 - Hubble went looking for Cepheids in other bright galaxies ○ We can call them that now... ○ And he found them - Also looked at brightest stars, other "distance indicators"

Cepheid Distances

- Cepheids are bright and rare ○ Have to calibrate distance scale ○ Need distances to some Cepheids ○ Used to be indirect; now have parallaxes - If you are wrong about Cepheids distances, you are wrong about everything else

Examples of Dwarf planets

- Ceres (Asteroid belt) - Pluto (Kuiper belt) · At least five moons (Charon, Nix, Hydra etc.) - Haumea (Kuiper belt) · Has two moons (Hi'iaka and Namaka) - Makemake (Kuiper belt) · Eris (Scattered disk) - Most massive dwarf planet, but smaller than Pluto. · One moon (Dysnomia) - Sedna

Circular motion

- Circular motion needs a force and Newton realised this and came up with this law. >> Just enough centripetal force Fc to balance the speed, just enough speed to balance the centripetal force

Classes of spectral type (temperature scale)

- Classes from O (>3000K in temperature) to M (<3500 K in temperature) - Classes are further subdivided from 0 (hottest) to 9 (coolest) - The sun is a G2 star

Ice in the Polar Cap (Mars)

- Contains mostly CO2, a bit of H2O - Brightest radar signal concluded to be the light coming from liquid water. - Melting point of water decreases under the pressure of an overlying glacier. - Water is special and increasing pressure = lower pressure. - Core of Earth is opposite where increasing pressure = increasing melt/freeze temperature. - Presence of salts on Mars further reduces the melting point of water liquid even at below freezing temperatures. - Water gets colder when salt is in the water (E.g. icicle of death) - Lowers freezing point (easier to freeze) Lake Vostok (Antarctica)

A history of Venus

- Core could be solid due to no magnetic field. - CO2 produced during outgassing remained in atmosphere (Unlike on Earth where it dissolved in water). - Any of the water present on the surface of Venus rapidly evaporated. - Water vapour is also a very good greenhouse gas and hence would start a positive feedback cycle. - The temperature would rise, vaporising anymore water on Venus into water vapour to form more greenhouse gases and hence a higher greenhouse effect and the surface temperature hotter. - The inorganic cycle on Earth did not get established on Venus which contributed to this runaway greenhouse effect.

What is Dark Matter? Cannot it just be gas and dust

- Dark Matter Cannot Just be ordinary matter that is not emitting light? ○ No, we would still see it ○ Either in emission if gets heated up ○ Or via absorption ○ Also constraints from the big bang - Dark matter could be Black holes, or "MACHOS" - but can't find enough of them - Plus, we don't how to make them So what is it? - Dark matter is likely to be a fundamental particle (new kind) ○ But can't be one we have already know ○ We know dozens of particles, so room for more ○ Many reasonable theories can explain dark matter ○ Needs to make up about 23% of the universe ○ Looking for it! § Direct detection experiments, particle accelerators (LHC), astrophysical evidence

Of the inner planets, Mercury is the:

- Densest - Oldest surface - Massive core - Has a magnetic field, like Earth (Mars and Venus o not have an internal magnetic field). Mercury: - Far too close to the Sun for surface to have liquid water. - Too low mass to hang onto any atmosphere. - Close orbit to Sun causes its resonant orbit. - Closest planet to the sun, but has water ice.

How Big is the Universe

- Depends on what you mean - Mathematically, an open or flat universe is infinite ○ But we can't see all of the universe - Light travels at a finite speed: 300,000 km/s - Naive answer: Edge of visible universe 13.8 billion light years ○ But stretched by expansion ~40 billion years ○ Numbers modified by dark energy and inflation, too.

Alexander Friedmann and Georges Lemaître

- Developed cosmological solutions to general relativity ○ Homogeneous and isotropic universe Einstein initially rejected paper... but reversed later on GL: - Expanding universe: 1927, began with: ○ "Primeval atom" ○ "Cosmic egg"

General Relativity

- Discovered in 1915 ○ Changes ideas of space and time (merges space and time into an object called space-time) ○ And is a theory of gravity (space-time is bent and curve by presence of a mass "microlensing") - "Matter tells space how to curve, and space tells matter how to move" - John Wheeler - Light moving in a straight line but becomes curved because of the gravity field star

Pluto facts (full summary)

- Distance from fun: 39.5AU - Iron, rock and ice - Orbital period 248 years. - Rotational period 6.4 days (tidally locked with its moon Charon). - 0.36 Earth diameters. - 1/500 Earth masses. - Still has an atmosphere despite being so small. Discovered by Clive Tombaugh · Has craters. (history of impacts) · Has ability to reform in some areas. (still fairly smooth) · The area which has been reformed is mainly made of; nitrogen ice, carbon dioxide ice and these flow like glaciers.

Uranus facts

- Distance from sun: 19.2 AU - Orbital period 84 years. - Rotational period 17 hours. - 8 Earth diameters. - 14.5 Earth masses. - Has rings. - Iron, rock, hydrogen - Rotation axis in plane of orbit due to something large that hit it in the past · Uranus tilt 98 degrees. · Gives extreme seasons due to this. · Has magnetic fields. (Aurorae) · Moons: · Ariel · Umbriel · Oberon · Titania · Miranda · Puck - Discovered by William and Caroline Herschel

Electromagnetic Radiation

- EM wave + EM particle (photon)= EM radiation · Light · Two important properties: Wavelength of light (how much energy the light carries), The intensity. • Shorter the wavelength, the more energy it carries Eg. X-ray, gamma rays, UV rays. • Longer wavelengths have small amounts of energy E.g. Infrared • Visible spectrum: 400nm ~ 700nm

Early universe matter

- Early universe has just a little bit more matter than antimatter ○ Electrons and positrons (and other, heavier pairs) annihilate ○ Wind up with a universe with more photons than electrons ○ And number of electrons matches number of protons - Neutrons and protons: ratio depends on temperature ○ One neutron for every seven protons at "freeze out" ○ Depends on mass difference; photon density ○ Free neutrons: key difference to stellar interiors

Nucleosynthesis

- Early universe is too hot to form nuclei ○ Deuterium (proton + neutron) is fragile, first thing to be made ○ So universe must cool for nuclear burning to begin ○ Prediction: the universe is 25% helium BY MASS ○Actually ~24% (some neutrons decay, plus other things)

The Atmosphere

- Earth had a primeval atmosphere from remaining gasses captured during formation of Earth. - Atmospheric composition severely altered (secondary atmosphere) through a combination of two processes: 1. Outgassing: Release of gasses bound in compounds in the Earth's interior through volcanic activity. 2. Later bombardment with icy meteoroids and comets.

orbit of earth to sun- richard

- Earth orbits sun in 1 year ○ Pluto: 248 years ○ ("Year") ~ (Radius)1.5 - Outer planets go further ○ And go more slowly... (due to lack of gravity from sun) Velocity of orbit is constant, doesn't die away with distant, weird- expect outer stars to orbit slower

Impact Cratering and its history

- Ejecta from the impact can be seen as bright rays originating from young craters. - Without an atmosphere or any plate tectonic activity, there are no processes like erosion or volcanism to erode or alter the moon's surface History of Impact cratering - Rate of impacts due to interplanetary bombardment decreased rapidly after the formation of the solar system. - Most craters seen on the moon's (and Mercury's) surface were formed within the first ~ half billion years.

4 Million Solar Mass Black Hole

- Ensures centre of our galaxy is a violent environment ○ Strong gravitational field ○ Huge accelerations - Radius of "event horizon" ○ ~60 million kilometres (well inside earth's orbit) ○ S0-2 does not come close enough to the black hole to be torn apart - Black hole never directly observed: but nothing else fits... Black holes and stars don't explain the radio or x-ray emission from the centre of the galaxy on their own... Galactic Centre also contains hot dense gas, emits radio and x-ray

Ancient Greek Astronomers

- Eudoxus (409 - 356 B.C.): Geocentric model of 27 nested spheres to explain planetary motion. - Aristotle (384 - 322 B.C.): Universe can be divided into two parts o Imperfect, the changeable Earth, at the centre of the Universe. o Perfect Heavens (described by spheres). He expanded Eudoxus' Model to Use 55 Spheres - Aristarchus (310 - 230 B.C.): Got correct order of planets and sun at centre of Solar system. Also believed that stars were other suns. (Idea rejected but is correct).

Cosmological Motion

- Expansion of the universe is different from regular motion ○ New space "created" as the universe expands ○ A homogeneous universe cannot have a "centre"

Saturn facts (full summary)

- Extensive ring system. - Ring appear edge-on to Earth every 15 years. - Orbital period 29.5 years. - Rotational period 17.25 hours. - 18.8 Earth diameters. - 95 Earth masses. - Has magnetic fields (they have Aurora). ring system: - Some of the gaps in Saturn's ring system are caused by orbital resonances with Saturn's inner moons. - Particles in the Cassini division orbit twice for every orbit of the moon Mimas. - This makes their orbit unstable, effectively causing the particles to take up a different orbit. - In the Enke gap, there is a ellipsoidal moon called Pan. - Titan · has an extensive atmosphere. · Lakes on Titan. · Not quite water, actually comprised of hydrocarbons: methane, ethane. - Mimas · Very old (has many craters) · Iapetus · Also a very old surface (craters) · Also has a seam (from collision) - Enceladus - New surface ( not many craters) - Smooth surface: tidal heating a surface into liquid, venting covers the old craters. · Some craters but not as many as Iapetus and Mimas. · Something must be reforming the surface since there are minimal amount of craters. · There is molecular hydrogen release coming out of the cold geysers. · Having geysers suggests that there is an internal heat source that liquefies the icy materials into water.

The Atmosphere, surface, craters of Venus

- Extremely inhospitable: (96% CO2, 3.5% Nitrogen and the rest is water, HCl and hydrofluoric acid. - Four thick cloud layers can be seen through UV image. - Has very efficient greenhouse - Very stable circulation with high speed winds (up to 240 km/h) - Has an extremely high surface temperature (745K = 472 degrees Celsius). Venus's Surface - Smooth lava flows. - Scattered impact craters (not as many as Mercury). - Volcanic regions Craters on Venus - Nearly 1000 impact craters on Venus. - Surface not very old. - No water on the surface; thick, dense atmosphere. · No erosion. - Evidence of volcanism

Numbers (Black hole merger)

- First merger observed: September 14, 2015 at 09:50:45 UTC - Distance from Earth: 420 Mpc; 1300ly (±30% in diastance) - 36+29 solar mass black holes progenitors that went into merge - 62 solar mass final state -3 solar masses worth of energy radiated

Ancient Greek Astronomy

- First preserved written documents about ancient astronomy are from ancient Greek philosophy. Greeks tried to understand the motions of the sky and describe them in terms of mathematical models. - Models were generally wrong because they were based on wrong "first principles". - But were the first to start finding reasons and models for the motion of the sky. Idea from Socrates (470-300 B.C.E.) and Plato(427-347 B.C.E.) · They came up with a model that the sky was rotating, the Earth is spherical.

The Moon: The view from the Earth

- From Earth, we always see the same side of the moon. - Moon rotates around its axis in the same time that it takes to orbit around Earth. - Tidal coupling: · Earth's gravitation has produced tidal bulges on the moon. · Tidal forces have slowed rotation down to same period as orbital period. · Has an elliptical orbit and so may sometimes appear bigger and brighter.

Galaxy Clusters

- Galaxies are not distributed randomly in space ○ But form clusters and groups - Milky Way and M31: big galaxies in the local group - Clusters - Clusters combine to form superclusters ○Local Group is part of the Virgo Supercluster

Active galaxies

- Galaxies contain millions, billions or trillions or stars ○ Intrinsically bright -- stars shine, after all. - But active galaxies generate energy at their cores ○Remember the centre of the Milky Way

Local Group

- Galaxies continue to merge ○ Velocity of M31 (andromeda, nearest galaxy to milky way) measured in three dimensions ○ Will merge with Milky Way in ~4 billion years - Left with a big galaxy in an empty universe ○ Stars eventually grow old and die ○ Gas and dust consumed ○Universe is "red and dead" (empty with no more star formation)

Dark matter? 2. Galaxy clusters

- Galaxies live in clusters and superclusters ○ Measure their velocities - Assume all matter in is stars ○ Going too fast to hold together... how fast can this object move and also be stable (finding out that a lot of them are moving too fast to be held together) - Back to Zwicky (1930s) - If clusters not "bound", they must be "chance gatherings" - But there are far too many of them for that... - Look for "missing mass" ○ Hot gas (not enough to explain it to be bound) - Works nicely for dark matter - Needs a new modification to gravity (scale of galaxy too small

What do we learn from LIGO detection?

- Gamma ray burst detected 1.8 seconds after gravitational wave signal ○ Speed of gravity = speed of light; ○ To within seconds in 140 million years - Strong evidence that gold (and other heavy metals) produced in neutron star interactions; not just supernovae! - Allows an independent measurement of Hubble's constant - Also kills lots of theories of "alternative gravity" that try to provide alternatives to dark matter

Milky Way: The Disk (spiral galaxy formation)

- Gas and dust concentrated in the disk - Star formation occurs in the disk (where we find young stars) - Star formation happens in open clusters ○ A few hundred stars, young, Population I ○ 10 to 40 ly across ○ Stars not evenly distributed in disk Probe different lines of sight (e.g. blue stars, gas in 21cm)

Earth's interior

- Gets hotter towards the centre. - Earth's core is as hot as the sun's surface (6000 degrees Celsius). - Earth's Inner core is solid despite being so hot.

geology and volcnanism of mars

- Giant Volcanoes - Valleys - Impact craters · Has a massive trench (Marianna Trench) · Reddish deserts of broken rock, probably smashed by meteorite impacts. Volcanism on Mars Olympus Mons: - The highest and largest volcano in the solar system. - Youngest volcano on Mars. - Volcanoes on Mars are shield volcanoes (shallow slope 5~6 degrees). - 21km above mean Mars surface.

Einstein- General relativity

- Given tools to consider accelerations. - Gravity is not a force but more due to curved/bent space time. - Objects "think" they feel a force of gravity but they are actually moving in straight lines. However, the space they move through is curved/bent hence appearing to move in a curved trajectory. - Curvature changes. Anything that is orbiting causes ripples in space time. - Einstein described gravity as a warping of space-time around a massive object. The stronger the gravity, the more space-time is wrapped. - Light travels along the curved space taking the shortest path between two points.

Four main stages of Evolution of solar system

- Gravitational collapse of proto stellar cloud, with disc. - Condensation of gas cloud to chrondrules. - Accretion of gas and dust to form planetesimals. - Accretion of planetesimals

Ripples (Black hole merger)

- Gravitational wave signals from two black holes orbiting each other (if the signal is constant then the ripples would be constant). - The gravitational waves take some energy out of the system ○ To pay for this the black holes move closer to each other (further down their potential wells) ○ This releases energy ○ Makes black holes speed up ○ Generate gravitational waves more efficiently ○ Radiate more quickly ○ Move even closer together ○ Will collapse into each other (merge) - Signal called a "Chirp" - Detect these signals with LIGO detectors ○ Bending and stretching of the signals Rainer Weiss devised LIGO (1970) and built from 1990s - 2015

Einstein- principle of equivalence

- Gravity = Acceleration - We cant tell the difference between when on earth with -9.8 downward gravity and when in space with +9.8 acceleration of upward thrust Zero gravity: You would feel weightless when you free fall on earth (ball at the top when you throw ball), as there is no acceleration, same as space with zero gravity

Temperatures: Heating, albedo and Greenhouse effects and escape velocity

- Greenhouse effect depends on composition of atmosphere and also on whether a planet can keep it's atmosphere. Therefore need to consider escape velocity. - Escape velocity is the speed that the particle must achieve in order to escape an object's gravitational pull. · Smaller mass= smaller escape velocity Eg. If you throw a ball up into the air, if you do not surpass the escape velocity, then the tennis ball will come back down. However, if you throw it so fast/hard that it exceeds the escape velocity, the Earth will not be able to pull the ball back own with its gravitational pull.

Great Debate - 1920

- Harlow Shapley - nebulae are "local" - Heber D. Curtis - nebulae are galaxies Sorting out Great Debate: - Key work: Edwin Hubble ○ Hubble Space Telescope ○ Rhodes scholar & Anglophile - Discovered Cepheids in M31 ○ Distance: ~million light years - 1923, Milky Way just one galaxy (Curtis correct)

Where we are now (ingredients of universe)

- Have a complete list of basic ingredients of the universe ○ Dark matter, dark energy, radiation, atoms (baryons) ○ Plus neutrino background - Often called "Concordance Cosmology" or Lambda-CDM - Big questions about nature and origin of dark sector

Jupiter facts (full summary)

- Have moons - Distance to sun: 5.2 AU - Orbital period 12 years. - Rotational period 10 hours. - 22.4 Earth diameters. - 318 Earth masses. - Composition: iron, hydrogen, rock - Has rings (but not as extensive as Saturn) - Has a magnetic field (aurorae, biggest in solar system) - Has a relatively small core. Pressure is so high that the hydrogen can become a metal (solid). moons: Io - ·closest to Jupiter · Highly volcanic (volcanic plume) · Hotspots on Io ( more surface activity) ·The cause of the volcanism on Io is due to the intense pull of the gravitational field of Jupiter ( differential gravity field) Europa - · striations. · Very few impact craters (new surface) · Due to the gravitational pull, the striations are actually cracks (surface constantly cracked) and the material from inside come through these cracks and form the cold brittle surface ice. · Hence, Europa does not have many craters (they have been covered over/ reformed). Plate tectonics seen due to tidal gravitational forces. Ganymede - · Solar system's largest moon. · Has an old surface, retains the impacts (very cratered). · Nothing gets rid of the craters (like how Io has volcanism and Europa has the ice). · Impact records of crater chains support the theory that comets are loose agglomerations of material. Callisto

Johannes Kepler

- Hired by Tycho to work out mathematical detail of his model (he however used Copernicus' model instead as he believed the Earth also orbited around the sun). - He could only model the solar system to fit Tycho's observations if: Kepler's law of orbital motion (applied to all orbits) 1. Planetary orbits are ellipses with the Sun at one focus. 2. A line between the planet and the Sun sweeps out equal areas in equal times. 3. (T1 / T2)^2 = (R1 / R2)^3 or comparing planets to Earth: (Orbital Period / year)^2 = (Distance from Sun / A.U.)^3 Eccentricities of Ellipses - Low eccentricities, the orbits are still very circular.

1. Temperatures of stars (planck and wiens law)

- Hot= bright - Warm= dim Planck's law - Planck's law describes the spectral density of electromagnetic radiation emitted by a black body in thermal equilibrium at a given temperature T - Emission of EM radiation us described by Planck's law - The peak of the spectrum depends on the temperature of the object -Higher temperature, lower wavelength, intensity increases Wien's law - A star's temperature is related to its colour. - If we know its colour we can calculate its temperature T= (3 x 10^6) / λ(max), where peark wavelength is in nanometers (nm) and temperature is in degrees Kelvin (K) - Or if we want to find the peak wavelength λ(max)= (3 x 10^6)/T -1 nm= 10^-9 meters

Age of the Universe

- Hubble's constant is not really constant ○ Expansion rate of universe slows down (at least without dark energy) ○ Measure Hubble's constant - compute age of the universe - Hubble got ~500 km/s/Mpc ○ Universe much younger than the sun. - Today: Hubble's constant ~70 km/s/Mpc (+ dark energy) ○ Universe ~13.8 billion years old ○ Just a little older than oldest stars (which is good)

Roots of Astronomy

- Human cultures realised the cyclic nature of motions in the sky (stone and bronze ages). - Monuments date back to ~3000 B.C. show alignments with astronomical siginificance - Monuments likely to be used as calendars or even to predict eclipses. Eg. Stonehenge, Big Horn Medicine Wheel

The evolution of solar type stars- Stars less than 8 solar masses (low and intermediate mass stars)

- Hydrogen burning, pp chain (proton-proton fusion chain process, Fusion into 2 hydrogen atoms into helium), happens in core of star 1. Proton + proton > deuterium (+ neutrino) 2. Dertrium +proton > helium-3 3. Helium-3 + helium-3 > helium-4 + 2 protons - Where does the energy come from? Some mass is converted into energy (E=mc^2) Evidence for nuclear fusion? Passage of neutrinos which exit the planet

The Scientific Method

- Hypothesis to explain an observation - Make a prediction - New Observations - Match? o Yes > Accepted theory o No > New hypothesis required. - A good theory will solve problems using the same pattern of reasoning or problem-solving strategy and opens up new areas of research. - Note it is different to using correlations (correlations may show higher chances but not 100% conclusive). - No matter how much evidence we have for a conclusion, the conclusion could still conceivably be false. Concept of falsifiability is key to science

dark matter? 4. Galaxy/cluster interactions

- If galaxies just made out of stars and gas, they can influence each other beyond gravitational forces - Two clouds of dark matter can just pass straight through each other - Win for dark matter

Distance Ladder- can also be used to infer size of universe

- If one rung is off, the rest will be out ○ Leads to systematic errors... ○ Many different, overlapping options ○ But all measurements involve several rungs - Hubble flow: bound objects don't expand ○ Observationally + theoretically - Can also infer Hubble's constant from observations of the microwave background

what are Constellations?

- In ancient times, constellation only referred to the brightest stars that appeared to form groups, representing mythological figures. - Stars of a constellation only appear to be close to one another because of the projection effect.

Redshift & Distance

- In the 1920s, Milton Humason took spectra of galaxies ○ Saw that galaxies were moving with large velocities ○ Some toward us, mostly away from us - Distant galaxies moving faster than nearby ones ○Seems as though the universe is expanding

Maori Astronomy

- Includes details of seasons and using the stars for navigation. Knowledge and understanding has been mixed with colonial knowledge and lost over the past two centuries.

Intermediate-mass stars (life line)

- Interstellar cloud (light-years across) - Collapses down to a proto-star - Starts main-sequence - Forms helium core, becomes red giant - Blue loop during helium burning - CO core, becomes AGB star - Dust driven mass-loss removes envelope - Forms a planetary nebula that slowly fades - Leaves a (carbon-oxygen) white dwarf remnant.

The snowline ( PAST TEST and EXAM HINT)

- Inward of snowline: blown away by solar wind, rocky, smaller - Away from snowline: solar wind not strong enough, higher gravitational force, sweep up more gas, larger

Dwarf Planets (full summary)

- Is in orbit around the sun. - Hass sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a nearly round (spherical) shape (due to hydrostatic equilibrium). · Vesta is a minor planet not spherical enough to be a dwarf planet - Has not cleared the neighbourhood of its orbit (it is not the biggest planet in its orbit). - Is not a satellite of another planet. - Planets get lumpier as they get smaller, materials crush them more - Ceres (Asteroid belt) - Pluto (Kuiper belt) · At least five moons (Charon, Nix, Hydra etc.) - Haumea (Kuiper belt) · Has two moons (Hi'iaka and Namaka) - Makemake (Kuiper belt) · Eris (Scattered disk) - Most massive dwarf planet, but smaller than Pluto. · One moon (Dysnomia) - Sedna

Speed of gas particles

- It is a distribution (some fast, some slow). - The higher the temperature the higher the average speed, the cooler the temperature the lower the average speed. - Fast moving gas particles can escape from a planet's atmosphere such as Hydrogen (higher than Earth's Ve). - Heavier molecules (O2, N2, H2O) move slower at the same temperature than lighter molecules (H2, He)

Complication of Black Body Radiation (inverse square law)

- It is mucked up by distance. - The energy we receive is inversely proportional to square of the distance. · The larger the distance, the larger the energy received. Inverse Square law (hint)

Other Evidence of dark matter

- It is not just supernovae ○ Detailed appearance of the microwave background ○ Evolution of galaxy clusters ○ "Baryon Acoustic Oscillations"

The Milky Way: Measuring its size

- Jacobus Kapteyn (1851-1922) ○ Parallax: Find the distances of nearby bright stars ○ Proper motion: stars appear to move relative to other stars ○ Closer stars appear to move more quickly than distant stars ○ Estimate the distance from spectral type - His conclusion ○ Milky Way 20,000 parsecs [65,000 ly] across ○ We're fairly close to the centre. (incorrect, ignored dust effects)

Redshift

- Light "stretched" in an expanding universe ○ Cosmological redshift different from kinematic redshift ○ All cosmological observers think they are at rest ○ Redshift is induced by the growth of the universe

Rotation and Revolution (Mercury)

- Like Earth's moon (tidally locked to revolution around the Earth), Mercury's rotation has been altered by the sun's tidal forces. - It is NOT completely tidally locked: Revolution period = 3/2 times rotation period. · 3 : 2 resonance · Mercury rotates 3 times on its axis in the time taken to go twice around the sun.

Oort and Lindblad

- Looked at proper motions and radial velocities ○ Radial velocity from red (or blue) shift ○ Concluded that the galaxy rotates (1927) ○ Deduced the structure of the Milky Way ○ Spiral arms, disk, bulge and halo... - Milky way contains lots of dust and molecular clouds ○ Reddens and obscures stars... ○(250 million years for sun to rotate galaxy)

Steady State

- Main "competition" for the big bang until 1960s [Hoyle] ○ Universe still expanding in steady state cosmology ○ But new matter created to keep density constant [by magic] ○ Appearance of universe unchanging: no age problem - Hoyle coined the name "big bang", so he did invent the name - Debate ends with discovery of microwave background (1965) ○ Except for Hoyle and a few others...

The Milky Way: Globular Clusters (How we found out we are not at the centre)

- Many globular clusters visible in the sky - Mostly 10s of 1000s of light years from earth - Harlow Shapley mapped distribution of globular clusters ○ Obtained distances from RR Lyrae variables ○ Although he initially thought they were Cepheids ○ [Cepheids discovered by Henrietta Swan Leavitt, 1908] ○ Gets distances wrong, but shape right - Using clusters, we're not in the centre anymore ( sun is not centre of the milky way because clusters are not centered around sun) - The Milky Way is about 100,000 parsecs in diameter

Hubble's Constant

- Measures how fast the universe is expanding - Measured: roughly ~70 km/s/Mpc ○ Mpc - mega-parsec, 1 million parsecs ○ If a galaxy is 100 Mpc away, 324 million light years ○ Receding at 70x100 = 7,000 km/s (kilometres/second) ○ Speed of light: 300,000 km/s - The Hubble Constant is the unit of measurement used to describe the expansion of the universe

Why inner core of Earth is solid

- Melting point is the temperature at which an element melts (transition from solid to liquid). - Melting point increases with increasing pressure toward the centre. - =inner core becomes solid · It gets to a point where the pressure is so great and the melting point is so great that it exceeds the temperature of the material in the core. · So it has an intense pressure but it is still not hot enough to melt the material at that high pressure. · Inner core becomes solid.

dark matter? Microwave background..

- Microwave background (to come) has hot and cold spots ○ Mix of spots matches predictions of dark matter - Ultra faint galaxies ○ As few a few hundred stars ○ But masses of hundreds of thousands of stars - Win for dark matter

Extrasolar Planets and the Habital zone

- Modern theory of planet formation linked to star's evolution o Many stars should have planets. o Planets orbiting around other stars are "extrasolar planets". - Cannot be imaged directly, look for 'wobbling' motion of the star around the center of mass HZ: Contains liquid water= supports life (0-100oc)

Primordial Nucleosynthesis

- Most nucleosynthesis happens in "first three minutes" ○ Almost all neutrons now in helium-4 atoms (stable state) ○ Small amounts of other atoms (helium-3, deuterium, lithium) ○ These amounts depend on "photon:baryon" ratio ○ Everything else made in stars (or via radioactive decay) - Know photon number-density today from temperature of CMB (cosmic microwave background) ○ Compute mass of atoms in universe: few % of total mass ○More (indirect) evidence for dark matter

Vera Rubin

- Most stars in center ○ But velocity ~ constant. ○ (Period) ~ (Radius) - Vera Rubin (1975-80) ○ Spiral galaxies: outer stars move faster than they "should"

Neutron star merger (to discover more of in future)

- Neutron star mergers most commonly associated with gamma ray bursts ○ Gravitational waves move at similar speed to speed of light ○Detected this through gamma ray burst and neutron star merge

Hidden water on Mars

- No liquid water on the surface as it would evaporate due to the low pressure. - Water could be existent in frozen conditions (re-watch simulation). - Little atmosphere = low atmospheric pressure = immediately begins boil (boiled off) = turns immediately into solid (ice) - Many geological features when viewed up close by rovers appear the same as river features on the Earth

What is Dark energy?

- Nobody knows: this is a deep mystery ○ Density does not change as universe expands ○ Consistent with energy conservation ○ Associated with "negative pressure" [like a stretched spring] - Seem to need a good idea... ○ May be explainable as a modification to gravity ○Or the interplay between quantum mechanics and gravity

The Early Universe processes

- Nucleosynthesis - The Cosmic Microwave Background - Inflation: universe undergoes expansion

What is a white dwarf star?

- One end result of a low-intermediate mass star's life - Composed mostly of electron-degenerate matter - Very dense. About mass of Sun, about size of Earth - No fusion reactions at core - Not very luminous (HR diagram), still hot, bluer

How is Hubble's constant measured

- One way: Start with Cepheids ○ Nearby Cepheids distances be measured with parallax - Cepheids found in galaxies which host supernovae ○ Establish distance to galaxies; calibrate supernovae ○ Supernovae themselves "standardizable", not standard. - Get Hubble's constant: 73.00 ± 1.75 km/s/Mpc ○ Second way: microwave background (to come)

Three Possible Universes: Closed, Open and Flat (How to tell them apart (is the universe going to expand forever?)

- Open: expand forever, flat: expand but less, closed=stop then collapse - How to tell them apart? ○ Measure average density AND Hubble's constant ○ For any value of Hubble's constant there is a critical density § Above critical density: closed, recollapse § Belowcritical density: open, expand forever § At critical density: flat, expand forever ○ Note: this picture is modified by dark energy

Neptune facts

- Orbital period 165 years. - Rotational period 17 hours. - 7.6 Earth Diameters. - 17 Earth Masses. - Has rings. - Observed by Galileo · Has massive dark spot (like Jupiter's big red spot) where there is a massive cyclonic storm occurring. · Has very strong (fastest) winds due to no turbulence.

dark matter? 3. Light Bending

- Orbits look Newtonian ○ But gravity really obeys Einstein's rules - Gravitational lensing ○ Light bent by gravity ○ Distant images distorted - Bent in Newtonian gravity too ○ More bending from Einstein ○ Prediction of general relativity Gravitational lensing - Strong lensing ○ Double images, arcs - Weak lensing ○ Distant galaxies "squashed" We can build a "lensing map" - Find mass distribution - Most mass is dark matter ○ Independent test ○ Same rules (of gravity) ○Find that the mass from lensing does not equal mass from galaxies- win for dark matter

Stellar parallax

- Parallax is the observed apparent change in the position of an object resulting from a change in the position of the observer. - Specifically, in the case of astronomy it refers to the apparent displacement of a nearby star as seen from an observer on Earth.

Distance: standard candles

- Parallax only works for nearby stars - However - if we know what type of star we are looking at then we know how bright it should really be. We can compare this value with how much dimmer it appears from Earth and use this to get a distance - How do we know what type of star it is? · We need to obtain a spectrum and compare it to other stars with similar spectra whose distances and intrinsic brightness we know · These types of objects are know as "standard candles" - Example: cepheid variables · Regular change in luminosity due to oscillations in size · Length of period is proportional to true brightness Remeber: if we know how bright they should be - we can infer their distance

CMB Discovery

- Penzias and Wilson: communications satellite technology ○ Sky "warm", same temperature wherever they "looked" ○ Assumed it was a problem with their electronics ○ Looking in microwave wavelengths (a few GHz) ○ Corresponds to 3Kelvin blackbody ○ Dicke & Peebles (Princeton) building receiver to look for CMB

Problems solved by "inflation"

- Period of accelerated expansion, just after the big bang ○ In fact, the universe could be "born" inflating ○ Universe grows (at least) 1030 times larger during inflation - Smooths out any initial bumps and lumps ○ Generates ripples via quantum fluctuations... ○No-one knows why inflation happens

Dark Energy Discover

- Perlmutter, schmidt, Riess Nobel prize physics 2011

"Dark Matter" in the Solar System

- Planets obey Kepler's Laws... (from observations) ○ Consequence of Newton's laws (explaining Kepler's law with theory) - Plus small corrections (newton says kepler's law are only exact for stars that only have 1 planet) ○ Planets pull on each other (if you have more than one planet) ○ Kepler's laws assume the planets only talk to the sun... (but not to each other) - Uranus discovered in 1781 by William Herschel ○ Do the laws of gravity work all the way to Uranus? Or obeying different laws

History of discovery of extra solar planets:

- Prior to 1992: only solar system planets 1995: first confirmed discovery of a planet around a normal star

Quasars and AGN

- QSO (quasar): Quasi-stellar radio source ○ Point-like; discovered in radio, late 50s + early 60s ○ Associated with high redshift optical sources - Central engine of an AGN is an accreting black hole A quasar is a type of AGN Quasars is the term applied at the beginning, when the first objects of this type have been discovered. They were radio-loud and point-like (the so-called quasi-stellar radio sources).

Radio

- Radio waves generated by moving (accelerated) charged particles ○ Electromagnetic waves in general - Sag. A brightest source in radio sky (lots of movement) ○ At long wavelengths ○ Something is moving electrons - that something is not just stars because stats dont just produce radio waves

What the Universe is Made of? and dates

- Relativistic astrophysics (black holes, pulsars, quasars...) ○ Late 1950s through to the present day... - Dark matter ○ Hints in the 1930s; confirmed (for most of us!) in the 1990s - Dark energy ○ Discovered in 1998 ○ 70% of the universe is dark energy

Habitable zones

- Right temperature for liquid water - Need to consider other things such as; magnetic fields, change in atmosphere over the years, plate tectonics

Mars and its atmosphere (full summary)

- Rotation period = 24h 40 min - Very thin atmosphere (mostly CO2) - Diameter is approx. 1/2 of Earth's diameter. - Mass is 0.1 of Earth. - Axis tilted against orbital plane by 25 degrees, similar to Earth's inclination of 23.5 degrees. - Seasons similar to Earth: Has the growth and shrinking of polar ice cap. - Crust not broken into tectonic plates. - There has been volcanic activity in the past (including highest volcano in the solar system) possibly ongoing. The atmosphere of Mars - Very thin: Only 1% of pressure on Earth's surface. - 95% CO2. - Due to the tiny mass, the surface gravity is too low to hold onto a thick atmosphere. - Can see thin Martian atmosphere through a haze and clouds covering the planet. · There is a magnetic field but it is not strong like on Earth and Mercury. · Nasa' maven mission: how the solar wind is stripping Mars of its atmosphere (presence of Aurora) - Can sometimes see dust storms. - Giant Volcanoes - Valleys - Impact craters · Has a massive trench (Marianna Trench) · Reddish deserts of broken rock, probably smashed by meteorite impacts. Volcanism on Mars Olympus Mons: - The highest and largest volcano in the solar system. - Youngest volcano on Mars. - Volcanoes on Mars are shield volcanoes (shallow slope 5~6 degrees). - 21km above mean Mars surface. - No liquid water on the surface as it would evaporate due to the low pressure. - Water could be existent in frozen conditions (re-watch simulation). - Little atmosphere = low atmospheric pressure = immediately begins boil (boiled off) = turns immediately into solid (ice) - Many geological features when viewed up close by rovers appear the same as river features on the Earth - Contains mostly CO2, a bit of H2O - Brightest radar signal concluded to be the light coming from liquid water. - Melting point of water decreases under the pressure of an overlying glacier. - Water is special and increasing pressure = lower pressure. - Core of Earth is opposite where increasing pressure = increasing melt/freeze temperature. - Presence of salts on Mars further reduces the melting point of water liquid even at below freezing temperatures. - Water gets colder when salt is in the water (E.g. icicle of death) - Lowers freezing point (easier to freeze) Lake Vostok (Antarctica)

Spiral galaxies + Elliptical Galaxies + Dwarf/Irregular Galaxies

- Same disk/bulge/halo structure as the Milky Way ○ Gas and dust in the arms ○ Continuous star formation - Spiral arm structure (no surprise there) e: - Little gas and dust ○ No ongoing star formation ("red and dead") - old stars ○ Stars orbit at all angles ○ No spiral arms - Most massive galaxies known are ellipticals ○ Range from 107 - 1013 solar masses - Giant elliptical: typically at the centre of clusters (to come) d/i: - Dwarf galaxies are small (no surprise) ○ 1% of the mass of the Milky Way (or less) ○ Fewer stars, so hard to see at great distances - Irregular galaxies are irregular [Not very imaginative names] ○ Can be rich in gas and dust ○ No fixed shape ○ Often disturbed by interactions with larger galaxies

Orbits and Spheres

- Satellites further from the earth or planets further from the sun ○ Move more slowly in their orbits - What if you could have an orbit inside the earth? ○ Only the fraction of the earth "inside" the orbit matters ○ Speed would be smaller than for an orbit at the surface ○ Assuming the earth has a constant density ○ Same with a galaxy...

What we learn from hubble constant

- Shape of the curve... ○ Expansion rate of the universe accelerating today ○ But was slowing down in the past (billions of years ago) - Consistent with a cosmological constant or "dark energy" ○ Idea of a cosmological constant is old (1920s)- added to general relativity to stop idea of universe expanding ○ Einstein's "biggest blunder"

The Milky Way: What Shape is it?

- Sir William Herschel & Immanuel Kant ○ They concluded that the milky way had to be disk shaped collection of stars ○ A couple of incorrect assumptions ○No consideration of dust effects because dust absorbs light

What we see of sky

- Sky is Temperate: 2.7 Kelvins - Temperature differences: parts in 100,000 - "Foreground subtraction" - hot gas, dust - Signal:noise > 100:1 at large scales ○ And it reflects the history of the universe - CMB First (knowingly) detected in 1965 ○ Each point in the sky ~3 degrees above absolute zero ○The universe is slightly "warmer" than expected

Current Understanding of Galaxies (how galaxies form)

- Small galaxies form first ○ Big galaxies form from mergers of small galaxies ○ Galaxies can merge - Galaxies seen at a redshift of 8 ○ ie wavelength stretched by a factor of 8 ○ Seeing them ~hundreds of millions of years after big bang ○ Universe 10-20 times younger than it is today

Gaps in Saturn's ring system and the Moons

- Some of the gaps in Saturn's ring system are caused by orbital resonances with Saturn's inner moons. - Particles in the Cassini division orbit twice for every orbit of the moon Mimas. - This makes their orbit unstable, effectively causing the particles to take up a different orbit. - In the Enke gap, there is a ellipsoidal moon called Pan.

Newton's World

- Space and time ○ Label "where" and "when" things happen - But are just co-ordinates ○ Not part of the "action" - Forces and rules of motion (tells us how objects will move) ○ In particular: gravity

Types of Galaxies: differ mainly in shape

- Spiral galaxies - Elliptical galaxies - Irregular galaxies

size of star and its evolution time + candle analogy

- Stars spent most of their time on main sequence (mass determines where they are on the main sequence), when they run out of fuel at the core, they evolve towards the right seuqnece into red giants, redder (lower temperature) - All stars formed roughly same time but they all have different masses, larger stars evolve off main seuqence faster, burn their fuel at the core sooner, by looking at a globular cluster we can give an age for that custer due to a similar birth date - Red= 1 Mega year (1 million year), blue= 10 million years etc... - The heavier the star= less time spent on main sequence

Conclusions for galaxies

- Stars, galaxies seem to be moving faster than we can account for just from gravitational fields of the stars - Galaxies (all galaxies) appear to be embedded in a dark halo ○ Halo extends well beyond the visible part of the galaxy ○ Dark fraction ~80% of total mass § And sometimes higher: ultra-faint galaxies □ As few as 100s of stars □ But a million solar masses - rest is dark matter □ Gas (to make stars) can be stripped by interactions

Galaxies evolve with time

- Stellar populations get older ○ With no star formation, only small old stars left (ellipticals) - Old stars return gas to interstellar medium ○ Either by supernova explosions ○ Or stellar winds (see planetary nebula) ○ Chemical composition changes with time ○ Process is nuclear physics, not chemistry

What the Universe Looks Like? galaxy

- Structure of the Milky Way Galaxy and our place within it ○ 1700s - 1930s - One galaxy or many? ○ Settled in 1920s - Large scale structure: stars live in galaxies; how are galaxies arranged in space... ○ 1980s - now...

There is a cycle for sun spots: Period of 11 years.

- Sun goes through busy and quiet times (sometimes it is more magnetically active than others, more sunspots= more solar magnetic activity - Sun is dynamic cycle, magnetic fields correlate to number of sunspots

Loops

- Sunspots arise from interactions between intense magnetic field and material on surface of sun - Magnetic field coming out of surface of the sun looping out of sun (N) and to surface of the sun (S) - Loops of plasma follow the magnetic field lines through the sunspots via the photosphere - Loops slow down the Convection loops in the convection zone (which transported in these loops), the magnetic loops poking through the photosphere , the convection transport gets suppressed so no more rising of materials= leaving sunspots - Material trapped in the magnetic field lines forming the prominences

dark matter? 5. Structure formation

- Take a box of dark matter and as it evolves, it forms a cosmic web structure that resembles our galaxies - With gas and toms, there is more pressure= less prone to collapse into this structure

How the Universe Changes With Time

- The expansion of the universe ○ Discovered in 1929 - The Microwave Background and Confirmation of the Big Bang ○ Discovered in 1965 ○ Microwave background is that the atmosphere is slightly warm 2.7 kelvin above absolute zero - Understanding the physics of the very early universe ○ 1940 - through to today

The fusion processes at centre of sta

- The fusion processes at centre of star, depends temperature and pressure of core of star, depennds strongly on mass of star (how much gravity is pulling matter into core of the star, changing pressure and temperature), drives what fusion reactions can occur at core of star and drives which elements can be mashed together to form additional energy What quantities at the centre of a star dictate what fusion reactions can occur? - Temperature - pressure

Different Kinds of Atoms

- The kind of atom depends on the number of protons in the nucleus. - Most abundant: Hydrogen (H), with one proton ( +1 electron), Helium (He) with 2 protons ( +2 neutrons +2 electrons) · Isotopes are when there are different number of neutrons but same number of protons. Number of protons determines type of element (HINT)

Roche Limit

- The radius around a celestial body (planet, star etc.), within which a second body held together only by gravitational forces will be torn apart by tidal gravitational forces. - Sets a boundary of which moons can form around planets before getting ripped apart by the planet's gravity - Hence we find the ring system between the planet and the moons. · There are a few exceptions of which can exist inwards of the Roche limit. e.g. Cordelia, Ophelia - Forces other than gravity hold these planets together

Radio Astronomy

- This method is used because it is hard to see through the dust in the milky way - Radio invented in the 19th century ○ Tesla, "Hertzian waves", Marconi, even Rutherford - 1930s: Karl Jansky founded radio astronomy ○ Need directional detector (sensitive to a particular direction) ○ Or timing as the source rises and sets ○ Or when source passes behind the moon (quasars, 1963) Brightest source at "low" frequencies: Sagittarius A

The Hot Big Bang

- Timing of nucleosynthesis ○ Depends on "photon to baryon" ration ○ Baryons- neutrons and protons - Early universe: exactly same amount of matter and antimatter ○ Complete annihilation; only photons left ○ But matter dominates by one part in a billion ○No one knows why..

Moons of Saturn

- Titan · has an extensive atmosphere. · Lakes on Titan. · Not quite water, actually comprised of hydrocarbons: methane, ethane. - Mimas · Very old (has many craters) · Iapetus · Also a very old surface (craters) · Also has a seam (from collision) - Enceladus - New surface ( not many craters) - Smooth surface: tidal heating a surface into liquid, venting covers the old craters. · Some craters but not as many as Iapetus and Mimas. · Something must be reforming the surface since there are minimal amount of craters. · There is molecular hydrogen release coming out of the cold geysers. · Having geysers suggests that there is an internal heat source that liquefies the icy materials into water.

Lunar surface features

- Two different kinds of terrain can be seen. 1. Highlands: mountainous terrain, scarred by craters, older surfaces. 2. Lowlands: 3km lower than highlands; smooth surfaces (dark and called Maria). Would have been basins flooded by lava flows during the formation of the moon.

Proton-proton fusion chain process: + Neutrino properties

- Two hydrogen nuclei (protons) fused together in a fusion reaction > making detirm + positron (1 proton + 1 neutron) + neutrino + energy When does this reaction twice in 2 separate reactions, 4 protons > 1 He nucleus (2 protons + 2 neutrons), find that the He nucleus slightly lighter as some mass has been converted into energy (E=mc^2), this energy powers the sun Neutrino: - Neutrino doesn't react strongly with other materials So when neutrino gets produced in fusion reaction, it leaves the sun immediately

Venus and Mars

- Two most similar planets to Earth. - Similar in size and mass. - Same part of the Solar system. - Has atmosphere. Similar interior structure.

Thermal history of the universe

- Universe cools as it expands ○ So: very early universe was very hot and very dense - Work out the thermal history of the universe ○ Allows us to learn how the universe evolves with time - in theory ○ Check against observations Everything melts:

Useful Numbers...

- Universe is roughly 13.8 billion years old ○ Sun is ~4.6 billion years old - Nearest big galaxies millions of light years away ○ Our galaxy ~100,000 light years across ○ Hundreds of billions or trillions of stars in a big galaxy

Relativity and Cosmology: 1920s

- Up until 1915, gravity had been described by Newton's laws ○ No-one had talked about an "expanding universe" - After 1915, ○ de Sitter, first paper on cosmology [with hindsight] 1917 - Einstein, 1920s - Einstein tries to build an infinite, static universe ○ Realises it won't work ("greatest blunder") - Even if the universe begins at rest, gravity sets things moving ○ Adds a "cosmological constant" term ○ Allowed by the math, but not otherwise required

orbit of venus (full summary)

- Venus rotates clockwise, with period slightly longer than orbital period - Possible reasons: · Off center collision with massive protoplanet · Tidal forces of the sun on molten core - Extremely inhospitable: (96% CO2, 3.5% Nitrogen and the rest is water, HCl and hydrofluoric acid. - Four thick cloud layers can be seen through UV image. - Has very efficient greenhouse - Very stable circulation with high speed winds (up to 240 km/h) - Has an extremely high surface temperature (745K = 472 degrees Celsius). Venus's Surface - Smooth lava flows. - Scattered impact craters (not as many as Mercury). - Volcanic regions Craters on Venus - Nearly 1000 impact craters on Venus. - Surface not very old. - No water on the surface; thick, dense atmosphere. · No erosion. - Evidence of volcanism - Core could be solid due to no magnetic field. - CO2 produced during outgassing remained in atmosphere (Unlike on Earth where it dissolved in water). - Any of the water present on the surface of Venus rapidly evaporated. - Water vapour is also a very good greenhouse gas and hence would start a positive feedback cycle. - The temperature would rise, vaporising anymore water on Venus into water vapour to form more greenhouse gases and hence a higher greenhouse effect and the surface temperature hotter. - The inorganic cycle on Earth did not get established on Venus which contributed to this runaway greenhouse effect.

Mercury (full summary)

- Very similar to Earth' moon in several ways: · Small, low mass so therefore, no atmosphere. · Lowlands flooded by ancient lava flows. · Heavily cratered surfaces. - Like Earth's moon (tidally locked to revolution around the Earth), Mercury's rotation has been altered by the sun's tidal forces. - It is NOT completely tidally locked: Revolution period = 3/2 times rotation period. · 3 : 2 resonance · Mercury rotates 3 times on its axis in the time taken to go twice around the sun. - Very similar to Earth's moon. - Heavily battered with caters, including some large basins. No wind, water, plate tectonics > means there are no erosive forces > the surface must be OLD.

The Surface of Mercury

- Very similar to Earth's moon. - Heavily battered with caters, including some large basins. No wind, water, plate tectonics > means there are no erosive forces > the surface must be OLD.

What is at work on the Galilean Moons (Jupiter Moons)

- Volcanism - Venting of water or frozen mixtures of carbon and hydrogen - Impact craters - Push me pull me gravitational stress - Plate tectonics (in case ice fracturing and folding)

The Milky Way: Stellar Populations

- Walter Baade noticed that: ○ The position and colour of stars in other galaxies correlated ○ Blue stars in the disks and spiral arms (Population I) ○ Redder stars in the central bulge and halo (Population II) 'metal'= anything not hydrogen or helium

atmosphere of venus

- We can work out models of atmospheres and calculate their temperatures and calculate their temperatures. - All stmospheres are warmer near the surface due to greenhouse effect. Venus has the densest atmosphere so it has the strongest effect - Venus is hottest not because it has the most CO2 but because it has the densest atmosphere

Absolute magnitudes

- We measure the brightness of a star (m) - We also measure its parallax (p) - We put all the stars at a distance of 10pc and then see how bright they are - 10pc corresponds to a parallax of 1/10 or 0.1 arc seconds. - These magnitudes are called absolute magnitudes (Mv) - At 10pc the Sun is a very ordinary star of absolute magnitude 4.6. - The brightest stars maybe at magnitude -10 or 3 lots of 100 (100^3) or a million times brighter. - The faintest stars may be at magnitude 15 or 100 x 100 fainter or 10,000 times fainter than the Sun. For example, the Sun has apparent magnitude of -27. At 10 parsecs: M(sun)= -27 - 5 log(4.8×10-6) + 5 = 4.6

Sky is not completely black at night...

- We see some spots of light (stars) ○ Now imagine the "galaxy" was infinitely large ○ And infinitely old, and with no gas or dust ○ With the same density of stars everywhere, at all times. ○ Then there would be a star wherever you looked - Olber's Paradox ○ if stars are distributed evenly throughout an infinite universe, the sky should be as bright by night as by day, since more distant stars would be fainter but more numerous. This is not the case because the universe is of finite age, and the light from the more distant stars is dimmed because they are receding from the observer as the universe expands.

Sun Spots

- When the sun is slightly more active - Correspond to Slightly cooler spots on the sun that appear darker

Galaxies Evolve

- Will see that the universe is around 13.8 billion years old ○ Galaxies billions of light years away younger than Milky Way - Study evolution of galaxies by looking deep into space ○ Although distant galaxies are very faint - Hubble Extreme Deep Field [25 September 2012] ○ 50 days of telescope time ○Most visible light shifted into the infrared

Do Distant parts of the Universe move faster than light?

- Yes, it seems so - but we can't see them ○ If recession velocity is greater than light, light can't reach us

Are the distant stars also fainter?

- Yes, that is certainly true ○ The inverse square law... - But there are also more distant stars ○ And the two effects cancel out ○So in an infinite universe, the night is as bright as the day... What Can We Do About This? - Assume the universe has a finite age ○ Speed of light limits how far we can see. ○ That will work

Hubble's Law

- a law stating that the red shifts in the spectra of distant galaxies (and hence their speeds of recession) are proportional to their distance

Hubble telescope

- detect far away galaxies - 2.4 metre mirror telescope - Observe in the near ultra violet, visible and near infrared spectra wavelengths - Important= be very familiar with the EM spectrum

Cosmic Distance Ladder

- each method forms a "rung" on the cosmic distance ladder, allowing us to calculate distances across the entire Universe!

Hubble- galaxies theory that is false

- thought that galaxies grew in a sequence (not just stay elliptical for the whole life) Thought galaxies were in a evolutionary track

Isaac Newton (1641 - 1727) and 3 Laws of Motion

1. A body at rest remains at rest. A body moving in a straight line maintains a constant speed and the same direction unless it is deflected by a force (Qualitative). 2. Or the acceleration of an object to which a force is applied is equal to the magnitude of the force divided by the mass of the object. Big force = Big acceleration (Quantitative). F=ma 3. Forces exist in pairs. Every force has an equal and opposite reaction. (Both Quantitative and Qualitative) E.g. Your weight pushes down on your chair which pushes you back up with exactly the same force hence you do not fly up to the ceiling or fall to the floor.

Kirchhoff's Laws of Radiation

1. A solid, liquid or dense gas excited to emit light will radiate at all wavelengths and thus produce a continuous spectrum. 2. A low-density gas excited to emit light will do so at specific wavelengths and thus produce an emission spectrum. 3. If light comprising a spectrum passes through a cool, low-density gas, the result will be an absorption spectrum.

The Solar Nebula Hypothesis

1. Big cloud of gas and dust collapses inwards due to gravity 2. Flattens into a disk, majority is mass in the gas cloud is in centre, becoming hotter and more dense, becoming the sun. outwards of the disk, planets will form. Sun and planets were formed from the same original materials 3. At some point the centre will get hot enough, the sun will 'turn on', fusion reactions will start and sun will start to produce energy, sun will push out solar wind, volatile materials will then evaporate. Therefore there is less stuff near the sun (smaller planets) and more stuff away (bigger planets, ice still remains) - Basis of modern theory of planet formation. - Planets form at the same time from the same cloud as the star - Planet formation sites seen today as dust disk of T tauri stars - Sun and solar system formed 5 billion years ago

Two ways of taking survey of stars in an astronomical survey

1. Brightness-limited - Only sees stars that are either very close, or are very big. 2. Distance/volume-limited - Gives a better deduction as it takes in all stars within that distance.

Why build big telescopes? high up?

1. Collecting area 2. Resolution · Waves spread out. (light is a wave) · Bigger telescope= collect more spread 1. Atmospheric absorption · The atmosphere absorbs light. Hence, it must have an effect on the light. · The atmosphere also absorbs gamma rays, x-rays, UV and Infrared spectrum · The atmospheric gases also absorb most of the infrared spectrum. · Long wavelenth radio waves blocked · Visible light is observable from Earth, with some atmospheric distortion 2. Atmospheric distortion - Atmosphere refracts starlight in random directions very quickly (which is why stars twinkle) and multiple images can be created. - On mountain tops, there is less atmosphere to look through= have less distortion.

Two kinds of matter: dust and radiation

1. Dust - Stars and galaxies - Not (or slowly) moving ○ No pressure - Density= 1/volume 2. Radiation: Photons - Moves at speed of light - Significant pressure - Redshifts with expansion ○ Energy/photon drops ○ Photon density= 1/volume ○ Energy density drops faster than volume increases

Low-mass star (life line) (more to the right of HR main sequence)

1. Interstellar cloud (light-years across) 2. Collapses down to a proto-star. 3. Starts main-sequence. 4. Forms helium core, becomes red giant. 5. Dust driven mass-loss removes envelope. 6. Forms planetary nebula that slowly fades. 7. Leaves a (helium) white dwarf remnant. -The universe is not old enough to have had this happen as of yet.

High-mass star (life cycle)

1. Interstellar cloud (light-years across) 2. Collapses down to a proto-star. 3. Starts main-sequence. 4. Forms helium core, becomes red giant. 5. Blue loop during helium burning. (He>CO) 6. CO core, burning stages continue to iron-group elements core. 7. Star explodes in a core-collapse supernova. (run of reactions to sustain itself, release of gravitational energy) 8. Leaves neutron star or black hole.

Two sources of heat in Earth's interior

1. Potential energy from material falling into the Earth (Gravitational potential energy turning into kinetic energy). 2. Decay of radioactive material (decay of such material produces heat). Most traces of bombardment (impact craters) now destroyed by later geological activity

But why was the Earth thought to be stationary (Greek)?

1. The Earth is not part of the heavens (today we know it is one of 8 planets and our sun is quite ordinary). 2. The celestial objects are bright points of light while Earth is an immense nonluminous sphere of mud and rock. 3. The Greeks saw little change in the heavens while Earth was the home of birth, change and decay. Finally, our senses show that the Earth appears to be stationary; There isn't a strong wind that we should technically feel since the Earth is rotating so fast.

Human effects on Earth's atmosphere

1. The greenhouse effect - Earth's surface is heated by the sun's radiation. - Heat energy is re-radiated from Earth's surface as infrared radiation. - Greenhouse gases such as H2O and CO2, but also other gases in the atmosphere, absorb infrared light (heat is trapped in the atmosphere).= greenhouse effect - It occurs naturally an is essential to maintain a comfortable temperature on Earth. - Without greenhouse gases, the Earth would be about 33K colder on average. - However, human activity, in particular CO2 emissions from cars and industrial plants, is increasing the concentration of greenhouse gases. 2. Destruction of the Ozone layer - Ozone (O3) absorbs UV radiation (which has damaging effects on human and animal tissue). - Chlorofluorocarbons (CFC's) which are used in industrial processes, refrigeration and air conditioning, destroy the ozone layer.

1st Law of Black Body Radiation

1. The hotter an object is, the more luminous it is: Luminosity strongly dependent on temperature to the power of 4 Where A = surface area Sigma = Stefan-Boltzmann constant L = Luminosity T = Temperature

Planets are discovered by (mainly):

1. Transit technique - Light from host star becomes periodically blocked by the planet orbiting around it. 2. Radial Velocity · Light from a star gets blue shifted (towards shorter wavelengths (higher velocity), towards you) and red shifted (towards longer wavelengths, away from you). · If the source in relation to observer is moving towards you the sound/light increase frequency and if move away it will decrease frequency 3. Microlensing (wikipedia) - Light from a distant star is bent and enhanced by the gravitational field of a closer star. The presence of an exo-planet rotating around that closer star bends the light of the star farther away periodically. 4. Direct imaging take a direct image of the planet.

Blackhole: how to detect them

1. observing the accretion disk- x rays, materials falling into blackhole forming amount of energy 2. Gravitational microlensing - Gravity can distort background light, we can detect this distortion 3. Companion stars orbits 4. Gravitational waves- emitted from inspiral of two neutron stars

types of telescopes

1. radio telescopes · Can detect magnetic fields basically. · A radio telescope reflects radio waves to a focus at the antenna. Because radio wavelengths are very large, the radio dish must be very large . · Interferometry (resolution trick) - Telescopes connected together to make an inferferometer can make even sharper images than a single large telescope if the interferometer is bigger than the large telescope. Images for same two stars are shown 2. Infra-red telescopes - is a telescope that uses infrared light to detect celestial bodies 3. X-ray telescopes - High energy photons reflect off a metal surface at shallow angles. A nested series of 2 or more cone-shaped reflectors focus the extreme- UV and X-ray light to make an image 4. Optical telescopes - is a telescope that gathers and focuses light, mainly from the visible part of the electromagnetic spectrum

2nd Law of Black Body Radiation

2. The peak of the black body spectrum shifts toward shorter wavelengths when the temperature increases. - Wien's Displacement Law: Wavelength decreases, temperature increases (bluer stars) (Where T(k) is the temperature in Kelvin).

A Dark Energy Dominated Universe and the future

A Dark Energy Dominated Universe -The universe will continue to expand (speeding up) unless dark energy has weird properties The future: Our Local Universe - The fraction of dark energy increases with time ○ Hubble's constant evolves towards a fixed value - Galaxies getting further away from each other ○ Apparent motion speeds up [over billions of years] - Eventually, distant galaxies would "move" faster than light (light emitted wont reach us) ○ And they become invisible ○ So after billions of years, only the local group will be visible

Types of Binary Stars- detection

A binary system is where two stars orbit a common center of mass. - Apparent binaries: Stars seen close together in the sky but not physically connected. - Visual binaries: Stars seen close together in the sky and ARE physically connected (not many). - Spectroscopic binaries: Stars seen as one but are physically connected. Only detected because of the velocity of one or both stars is seen to change. Most times only one spectrum is observed. Can detect motion of the stars. · Eclipsing binaries: Seen as one in the sky but rotate about a common centre. Only detected because each star in turn partially blocks the light from the other (one goes in front of the other).

Asteroids, Comets and Meteors/meteorites

A: In addition to planets, small bodies (asteroids, comets, meteoroids) orbit the sun C: - Icy nucleus which evaporates and gets blown into space by solar wind pressure - Mostly objects in highly elliptical orbits, occasionally coming close to the sun - Gets heated up by solar sun radiation, vaporized and pushed away by solar wind M/M: - Small (μm - mm sized) dust grains throughout the solar system - If they collide with Earth, they evaporate in the atmosphere. - Visible as streaks of light: meteors.

Chromosphere and Corona both seen in eclipse

Chromosphere: Layer above the photosphere Corona: Stream of plasma from sun

composition of the Sun

Composition: 71% hydrogen, 27% helium, 2% heavy elements

Discovery of gravitational waves

Confirmation of general relativity

Cosmology's Job

Cosmology studies the structure and evolution of the universe.... - Understand where the universe came from - Understand how the universe evolved ○ Understand how galaxies form ○ Understand how galaxies evolve and interact ○ Understand why stars (and planets) form ○ Understand when and where stars form ○ Explain what we see in the sky

Ways to look for dark matter- Direct detection, LHC, Astrophysical evidence

Direct Detection - Dark matter particles hitting earth ○ Interact weakly with regular matter ○ We are transparent to dark matter ○ And dark matter is transparent to us - Some dark matter particles interact ○ Detect recoiling atoms LHC "missing energy" -Make dark matter, have a collision by two particles -Since dark matter doesn't interact with regular particles, with collision a lot of stuff moving in one direction but not the other ("missing energy") Astrophysical evidence - Gamma rays from galactic centre

How to most massive stars die?

End result: neutron star orbiting each other (binary stars) > spiral inwards > releasing energy as they merge together > black hole

Newton's Law of Gravity (HINT, IMPORTANT)

G= gravity constant. M= mass of larger object. m= mass of smaller object. d= distance between objects Fg= force due to gravity Fg will be the same for both objects, but the accerelations will be different for the two objects (F=ma). The higher mass object will have smaller aceleration, whereas the lower mass object will have the larger acceleration (in order to have the same Fg)

Lecture 8 (23): star clusters

Google: Star clusters are groups of stars which are gravitationally bound. Two distinct types of star cluster can be distinguished: globular clusters are tight groups of hundreds of thousands of very old stars, while open clusters generally contain less than a few hundred members, and are often very young

Habitable Planets, planetary radius

Habitable Planets - Habitability is strongly linked to whether a planet can support liquid water on its surface. Planetary radius - Too small: planet loses atmosphere. - Too large: planet becomes a gas giant.

Heat and the Black Body Radiation

Heat: - Object becomes brighter with higher heat. - Hotter objects are brighter and "bluer" than cooler objects Black Body Radiation: - The light from a star is usually concentrated over a range of wavelengths. - The spectrum of a star's light is approximately a spectrum thermal spectrum called a black body spectrum. - A perfect black body emitter would not reflect any radiation. e.g. Black body radiation: Range of colours, radiates a range of wavelengths Only absorbs stuff at specific temperature Intensity: how much of that wavelength coming out of star 414 nm: very blue star (hot star, brighter, bluer) Cooler star= 725nm peak (much redder and dimmer and cooler)

2. Composition of stars: spectral lines

Hotter H gas: emits photon, Cooler H gas: absorb photon

4 Galileo Moons

Io - ·closest to Jupiter · Highly volcanic (volcanic plume) · Hotspots on Io ( more surface activity) ·The cause of the volcanism on Io is due to the intense pull of the gravitational field of Jupiter ( differential gravity field) Europa - · striations. · Very few impact craters (new surface) · Due to the gravitational pull, the striations are actually cracks (surface constantly cracked) and the material from inside come through these cracks and form the cold brittle surface ice. · Hence, Europa does not have many craters (they have been covered over/ reformed). Plate tectonics seen due to tidal gravitational forces. Ganymede - · Solar system's largest moon. · Has an old surface, retains the impacts (very cratered). · Nothing gets rid of the craters (like how Io has volcanism and Europa has the ice). · Impact records of crater chains support the theory that comets are loose agglomerations of material. Callisto

Stefan-Boltzmann Law

Luminosity is proportional to fourth power of temperature.

Stellar lifetimes

More massive stars die sooner (shorter lives)

Population 1 vs population 2 stars

Population 2 are from star-formation a long time ago, population 1 are from more recent star-formation

Scorecard

Score card for DARK MATTER 1. - Rotation curve doppler effect (1 and 1 for both modified gravity and dark matter) 2. Cluster dynamics ( win for modified gravity) 3. - Cluster lensing (win for dark matter) 4. - Galaxy/cluster interactions (win for dark matter) 5. Structure formation (win for dark matter) Assumption-dark matter= universe contains more stuff than we know Assumption modified gravity= gravity doesn't work as we think it does

Seismology

Sound waves passing through earth - Seismic waves do not travel through Earth in straight lines or at constant speed. - They are bent by or bounce off transitions between different materials or different densities or temperatures (More dense towards centre). - Such information can be analysed to infer the structure of Earth's interior.

Albert Einstein- special relativity theories

Special relativity (1): - Based on one assumption: that the speed of light is the same for ALL observers no matter how they're moving. Everything is moving at CONSTANT velocities under special relativity Special relativity (2): - E = mc^2 Energy has mass. When you move, you gain kinetic energy and hence increase in mass. However, by Newton's 2nd law, it would be more difficult to accelerate with higher mass. This is why it is not possible to travel faster than the speed of light.

Dark matter? 1. Rotation Curve Doppler Shift

Speed the galaxy is moving + contribution of gravity and halo

Stars evolution

Stars evolve over their lifetimes, they run out of hydrogen fuel and reconfigure themselves to star "burning" different elements to release energy. Their size and colour changes. This means that the same star appears at different places on a HR or CMD diagram at different stages of its life - Evolutionary track: up , as it runs out of hydrogen fuel to burn up into giant > across left> down to white dwarf (more red, less luminous) - Main sequence > giant star> white dwarf

Stellar nurseries and Nebula

Stellar nurseries - An area of outer space within a dense nebula in which gas and dust are contracting, resulting in the formation of new stars. Nebula - A nebula is an interstellar cloud of dust, hydrogen, helium and other ionized gases in a galaxy

Supernovae and Type 1 Supernovae

Supernovae - Exploding stars: briefly outshine an entire galaxy ○ So bright enough to be seen across the universe - Several types of supernovae ○ Type II: Giant collapsing stars - "core collapse" ○ Type Ia: Accreting white dwarf in a binary system - Chandrasekhar limit ○ Maximum mass of a white drawf- if over explosion Type 1a Supernovae - Type Ia Supernovae are roughly similar to each other ○ Peak brightness varies by 20-30%, Can be "corrected" to ~10% - One supernova / big galaxy / 100 years ○ Follow supernova to reconstruct light curve ○ Needs big telescopes / space telescope - Can find Hubble line from supernovae

Two Kinds of planets: 1. Terrestrial 2. Gas/ice giants

Terrestrial (Earth like, rocky, solid surfaces, closer to sun) 1. Mercury 2. Venus 3. Earth 4. Mars - Four inner planets of the solar system - Relatively small in size and mass (Earth is the largest and most massive) with Rocky surface - Surface of Venus cannot be seen directly from Earth because of its dense cloud cover Gas/Ice Giants (Jovian/Jupiter-like) 1. Jupiter 2. Saturn 3. Uranus 4. Neptune - Craters are not seen on Jovian planets because they do not have a solid surface. - Much lower average density. - All have rings (Not only Saturn). - Mostly gas; no solid surface.

Motions of Sky (Moon)- Solar and Lunar Eclipses

The illumination of the moon changes during its orbit of the EArth (due to sun) Solar eclipse when Moon comes between the Sun and the Earth (Shadow cast on earth by the moon ) Lunar eclipse: occurs when the Earth passes between the Moon and the Sun. • Shadow cast on moon by earth • The light gets bent when it goes through the atmosphere and this light is red. • Umbra is a full lunar eclipse (fully shadowed by Earth) Partial lunar eclipse called Penumbra.

nucleo synthesis summary

Thermal history of the universe - 10^-6 seconds after big bang: quark-hadron phase transition (temperature cool so goes from quarks to protons, neutrons) ○ Around 10 Trillion Kelvins ○ Protons and neutrons "melt" above this temperature - Universe contains hydrogen nuclei (protons), free neutrons, electrons and positions (anti-electrons) ○ Plus neutrinos, photons and dark matter ○ Nuclei are not stable, so no helium (2 H) Thermal equilibrium - A positron is an electron's antiparticle ○ A positron and electron can annihilate with each other ○ Total charge is zero ○ Electron + positron -> two photons (gamma-rays) - Two gamma rays can convert into a particle-antiparticle pair ○ If they have enough energy: "equilibrium" ○ As the universe cools, energy of photons drops ○ Eventually process goes one way For some reason (no-one knows why) - Early universe has just a little bit more matter than antimatter ○ Electrons and positrons (and other, heavier pairs) annihilate ○ Wind up with a universe with more photons than electrons ○ And number of electrons matches number of protons - Neutrons and protons: ratio depends on temperature ○ One neutron for every seven protons at "freeze out" ○ Depends on mass difference; photon density ○ Free neutrons: key difference to stellar interiors The Hot Big Bang - Timing of nucleosynthesis ○ Depends on "photon to baryon" ration ○ Baryons- neutrons and protons - Early universe: exactly same amount of matter and antimatter ○ Complete annihilation; only photons left ○ But matter dominates by one part in a billion ○ No one knows why.. Primordial Nucleosynthesis - Most nucleosynthesis happens in "first three minutes" ○ Almost all neutrons now in helium-4 atoms (stable state) ○ Small amounts of other atoms (helium-3, deuterium, lithium) ○ These amounts depend on "photon:baryon" ratio ○ Everything else made in stars (or via radioactive decay) - Know photon number-density today from temperature of CMB (cosmic microwave background) ○ Compute mass of atoms in universe: few % of total mass ○ More (indirect) evidence for dark matter Nucleosynthesis - Early universe is too hot to form nuclei ○ Deuterium (proton + neutron) is fragile, first thing to be made ○ So universe must cool for nuclear burning to begin ○ Prediction: the universe is 25% helium BY MASS ○ Actually ~24% (some neutrons decay, plus other things) The hot big bang - After a few minutes ○ Have protons, helium nuclei, electrons, neutrinos, photons - But can't (yet) make atoms ○ Photons so energetic they will ionize atoms they hit ○ Universe has to cool before atoms form ○ And a gas of protons and electrons is a plasma ○ Light cannot travel through a plasma (like the centre of a star) Recombination - Around 380,000 years after the Bang Bang ○ Universe cooled enough for hydrogen atoms to be stable ○ Universe now transparent ○ Called "recombination", really just "combination" - Microwave background photons can now move freely ○ Provides us with a "baby photo" of the universe

Neutron stars

These objects are what remains of the core of massive stars (10-30 solar masses) that have undergone stellar evolution, a core-collapse supernova and were massive enough after the supernova and were massive enough after the supernova explosion to contract beyond the white dwarf stage

Spectrum

Type of spectrum seen depends on the temperature of the thin gas relative to the background. (emission or absorption) Thin gas is cooler so absorption lines are seen in the visible spectrum. Thin gas is hotter here so only emission lines are seen.

Uranus/Neptune and Mercury Dark matter

Uranus and Neptune - Uranus' orbit did not match calculations - Adams and Le Verrier guessed there might be another planet.. And they were right ○ We knew the rules, but explained it by adding an extra planet Mercury - Under newton's laws, - "Perihelion percession" ○ Out by 43" of arc/century (based on maths) - Tried everything (could be a smaller planet closer to the sun, vulcan) - Explanation- New rules: General Relativity 1915 (change of understanding of gravity) Two examples of how to explain stuff in space we don't understand, changing understanding of gravity (mercury) or adding an extra planet (uranus)

Degeneracy pressure - white dwarfs and neutron stars made of degenerate matter

Where does pressure come from for remnants? - If remnant mass (left over after star's evolution) <1.4 masses, form white dwarf o Force pushing back against gravity= electron degeneracy pressure - If remnant mass( left over after's life on main sequence and fusion reactions) between 1.4 and 3 solar masses, forms neutron star o Crushed to more dense state, neutron star holds against material from gravity by neutron degeneracy pressure

Arabic, Indian, Chinese astronomy

arabic: - Al-Battani (CE 850-929,) made 4% error in measuring orbit of Earth around the Sun. Also made very accurate measurement of circumference of Earth indian: considerable expertise in observational astronomy. Most records lost in regligious Wars Chinese: Star exploded in 1006 (Supernova)

Three main types of stars of HR diagram

based on temperature and absolute magnitude), B-V= colour (smaller= bluer, larger=redder), longer wavelengths= redder colours, bluer= hotter, hotter= more massive (on main sequence) - Main sequence - White dwarfs - Giants/super giants - NEED TO KNOW AXIS AND ORDER OF THE VALUES, INDICATE ROUGHLY WHERE THE MAJOR GROUPS WHY DOES B-V EQUATE TO TEMPERATURE? - High mass stars= hotter, bluer - low mass= cooler, redder - Higher mass stars= shorter lifetime - Spectral class: O= very blue, hot massive, G= like the sun, M= red, small, cool - OBAFGEM Bigger mass= larger luminosity, brigher (absolute magnitude)

Reflectors (mirrors).

uses concave mirrors. light travels down the tube where it is reflected up to a secondary mirror near the top of the tube, which directs the light into the eyepiece.

Magnitude (m)

· 1 is brightest, 6 is dimmest (everything else falls in between). · Linear scale, each one magnitude is a factor of 2.512.

Outer planets compositions

· Are not all of the same type. - Saturn and Jupiter have similar compositions (mostly), but Neptune and Uranus are quite different to the other two gas giants.

Mounting

· Azimuth mount: centered wherever the observer is on earth Equatorial mount: accounts for earth's axis

Inner Solar Nebula

· Big ball of gas and dust begins to collapse from its own gravity. · It forms a disk like structure and begins to spin. · At the centre there is a strong over density of gas and dust getting hotter and more dense (eventually becomes the Sun). · Clumps of material orbit around the disk and these eventually become the planets. How solar system was formed 4.6 billion years ago

Copernicus (1473 - 1543 C.E.)

· Built on from Aristarchus' ideas where the Sun is in the centre and the planets orbit around it. - Problem was the parallax effect. The stars are too far for us to see the parallactic shift but people back then did not believe this before the use of telescopes and only believed that the Earth was stationary and hence thought this theory was wrong.

Formation History of Neptune and Uranus

· Core accretion theory cannot be used to explain the formation of these ice giants because: · The escape velocity of when they were proto planets (9km/s) is comparable to their orbital velocity (5km/s). · This similarity in speeds makes it really easy for the stuff in the orbit to go over their escape velocities and hence end up flying away off into space (disappears). - The material out where Uranus and Neptune are today, is relatively easily ejected through interactions with Jupiter and Saturn. This leaves too little material to build these ice giants. - Could have migrated. (HINT) · These planets may have formed closer to the centre (but outwards of the snowline) of the solar system and migrated out to their place after being formed. · Another theory is that these planets formed between Jupiter and Saturn and were then gravitationally scattered out of their present orbits. Formed in a protoplanetary disc and the streams of material pulls the planets towards or away from the sun.

Problem that ancient Greeks faced

· Earth overtakes in its orbit. · Mars appears to go backwards due to a projection effect due to Mars going slower in its orbit and Earth going past it. They did not know that Mars and all the outer Earth planets does this loop. Ptolemy (85 - 165 C.E.)- He explained that mars also moves in an epicycle as it orbits the Earth

Emission Lines

· Electrons emit light at one specific wavelength. (by jumping from higher energy orbit to lower energy orbit) · This is what occurs when emission line is produced

Pluto Surface

· Has craters. (history of impacts) · Has ability to reform in some areas. (still fairly smooth) · The area which has been reformed is mainly made of; nitrogen ice, carbon dioxide ice and these flow like glaciers.

Tides

· If we had no moon or stars, the oceans would be completely symmetrical all over the world. - However since we have the moon, the ocean gets drawn towards the edges and towards the moon and also in the opposite direction too. · We also have the Sun which causes spring tides and leap tides due to gravtational pull of the sun 1. When the Sun is at 90 degrees to the moon (Half phase)then there are weak tides. (low tide) 2. When the Sun and the moon are aligned (Full Moon/New Moon) then there are strong tides (high tide)

Refractors (glass lenses)

· Image is upside down. · Need to use convex lens as we try to use bigger lenses to capture more light. · Light rays go through the glass, different things are focussed at different wavelengths (chromatic aberration). · Only has one ray of light.

Earth zones

· Mantle (stiffer), outer core (solid), inner core (liquid). · These zones all have different densities (the physical matter changes at a boundary). · Can measure the size of the zones in comparison to one another by watching how the seismic rays pass through the Earth. - Eg. Earthquakes give good signals for this.

Heezen-Tharp Map (Tectonic plates) and history

· Mapped out sub-ocean ridges: these are regions where two tectonic areas are being forced apart and the hot mantle material is being forced up between the two gaps moving apart. History · Earth started off being a single land mass which spread around the Earth due to plate tectonics. · Can see this in fossil/species record. Creatures with the same ancestor can be explained if the areas of land was a single land mass in the beginning.

Galileo Galilei (1594 - 1642) and his discoveries

· One of the evidence is Planetary motion. - Reinvented the modern view of science: Transition from a faith-based 'science' to an observation-based scientific method. - Greatly improved on the newly improved telescope technology (Did not invent it). - First to report telescope observations of the sky to support the Copernican model of the universe. Major Discoveries of Galileo 1. Moons of Jupiter (4 Galilean Moons) 2. Rings of Saturn 3. Surface structures on the moon, estimates of the height of the mountains on the moon 4. Sun spots (proves that sun is not perfect). Phases of Venus, proving that Venus orbits the sun and not the Earth.

Degenerate matter

· Regular star: More mass = larger size. · Degenerate star: More mass = smaller size. - Because to hold up more mass you need more gravity to have more pressure against it. For degenerate stars you have to pack the particles closer together hence becomes smaller.

Magnitude Scale (1) (human scale)

· The more negative the magnitude, the brighter it is. - Brightest stars: ~1st Magnitude - Faintest stars (unaided eye): 6th Magnitude - 1st mag. Stars appear 100 times brighter than 6th mag. Stars. - 1 mag. Difference gives a factor of 2.512 in apparent brightness (Larger magnitude means fainter object). - Different set of wavelengths will mean different number for magnitude e.g. Mv = magnitude for visible light

Earth has magnetic field

· These are caused by circulating currents from the interior of the Earth. · Magnetic fields deflect the solar winds around the Earth. · Prevents the particles from the sun (radiation) from striking the surface of the Earth. · Magnetic fields can sometimes become trapped and strike the atmosphere at the poles of Earth. · When this happens, the gas becomes excited and then de-excites itself by emitting photons of light. You see this as an Aurora.

White dwarfs

· These stars are what remains of the core of low mass stars that have undergone evolution hence they are very hot. o These are compact objects with masses that of the sun but of sizes that of the Earth. o Nuclear reactions have stopped within them. o They are doomed to cool over billions of years. o Their cooling rates have given us independent estimates of the age of the universe. o Can explode in supernovae's.

Tidal Gravitational forces- Why do we only see one side of the Moon? What is with the 3 : 2 resonance on Mercury?

· This is because there is a distance dependence in the force due to gravity (differential gravity field). · One side of the plant feels a stronger gravitational field than the opposite side (the moon towards the Earth and Mercury towards the Sun). · The forces try to squeeze the force and material out, making a slightly oblate sphere. · It is non-spherical and hence, not symmetrical meaning a bit more mass in one particular direction. This means a higher force due to gravity will act on the bulge (extra mass). · So, when the moon and mercury try to spin in their own orbit, due to the additional forces from the Sun and Earth, they are unable to and hence keep facing the same way (mutually tidally locked= moon always facing earth with the same face, same with sun and mercury

Neutron star- conservation of angular momentum

· When a star shrinks down (from main sequence to neutron star) to a smaller size then it will spin up and faster. Low mass= high v, high mass= low v, angular momentum (p) conserved p=mv - angular momentum before (high mass, low speed) = angular momentum (low mass, high speed)

Stellar remnants (corpses of stars)

· White dwarfs · Neutron stars Black holes - Star start at main sequence uses fuel available depends on temeprature and pressure at core determines what nuclear reactions possible to giant and end - Energy is being released when consuming fuels (nuclear reactions) and that energy is moving outwards pushing against materials pushing into the star from gravity, a balance energy from nuclear reactions and gravity pushing materials into star - When the star runs out of fuel, there is no longer energy available pushing outwards from core to counter the gravity force towards centre of star. Gravity collapses inwards the centre until it forms one of these forms of degenerate matter

The Evolution of Massive Stars- stars more than 8 solar masses

Ø CNO cycle Ø Massive star > 10 solar masses= hydrogen > helium, helium > carbon, oxygen. CNO chain occurs only in massive stars temperature and pressure is high enough to allow fusion reactions to occur at the core Ø All produce energy due to loss in mass E-mc^2 Ø Heavier and heavier elements > Fe> supernova explosion Ø An alternative stellar lifecycle (no need to memorise, just need to know there are alternatives to how stars end their lives