Astro1000 Final Guide PDF

Topics We Have Studied This Semester Chapter 1: A Modern View of the Universe Our place in the universe and the hierarchy of structure: - Earth is one planet in… o What is the formal definition of a planet? o Why do dwarf planets like Ceres or Pluto fail to meet the definitio...

Topics We Have Studied This Semester Chapter 1: A Modern View of the Universe Our place in the universe and the hierarchy of structure: - Earth is one planet in… o What is the formal definition of a planet? o Why do dwarf planets like Ceres or Pluto fail to meet the definition? - The Solar System, which is independent of any… o Star systems may have more than one star in them. o Star systems are usually organized into pairs of binary stars. o The planets are tiny compared to the size of the solar system itself. - Star cluster, which are found in… o I mentioned two types of star cluster during lecture (open and globular). Can you compare / contrast the number, color, age of stars in each type? o Be aware that many stars not found in any star cluster (like the sun) used to be when they were first “born”. - The Milky Way galaxy, which is one galaxy in the… o Galaxy: a collection of star clusters and independent stars that orbit a common center point (now known to be a super-massive black hole). o The center of the galaxy is in the direction of the Sagittarius constellation. - Local Group galaxy cluster, which is one galaxy cluster that makes up the… o Major objects: Andromeda galaxy, Milky Way galaxy, Triangulum galaxy o Several dozen other galaxies (all significantly smaller than the big 3!). - Laniakea Supercluster, which is only one relatively small part of… - The entire universe, the totality of all energy and matter that exists. How to convert units, what units are useful in astronomy. - The astronomical unit (AU) - The light year (ly) 1  Look-back time: the further away astronomers look, the further back in time we are seeing due to light-travel delay. Chapter 2:Discovering the Universe for Yourself The celestial sphere - Stars are actually at varying distances from us, but look like they’re all painted on the celestial sphere! - Celestial poles and celestial equator: Earth’s poles and equator projected outward. - Ecliptic o Path of the sun across the celestial sphere over a year. o Actually plane of Earth’s orbit around the sun. o The planets are also found along the ecliptic. - The plane of the Milky Way galaxy is inclined to both the celestial equator and the ecliptic Constellations: imaginary patterns of stars along the celestial sphere. The local sky - Horizon: where the sky appears to meet the ground from your point of view. - Azimuth: where along the horizon (north/south/east/west) a star is located. - Altitude: how high above the horizon (in angular units) a star is located. Stars rise and set due to Earth’s rotation. Some stars are circumpolar; that is, they never set. The earth has seasons due to its axial tilt. - June solstice: longest day of the year in the northern hemisphere (summer), shortest day of the year in the southern hemisphere (winter). - December solstice: reverse of above. - Equinoxes: 12 hours of day and night everywhere on earth. 2  The phases of the moon - Phases caused by the moon’s changing position relative to the Earth-sun line as it orbits the Earth. o The sun always illuminates one side of the moon… o …But we can only see the side of the moon facing Earth. - Waxing vs. waning - Order: New, Waxing Crescent, First Quarter, Waxing Gibbous, Full, Waning Gibbous, Third Quarter, Waning Crescent. - Location of the moon in its orbit during each of the above phases. - What the moon looks like when seen from Earth in each of the above phases. Synchronous rotation; the moon spins on its axis in exactly the same amount of time it takes to orbit the Earth. Eclipses - Locations of Earth / sun / moon during a lunar or solar eclipse. - Why don’t we see an eclipse every month? - Phase of the moon during a lunar or solar eclipse. Chapter 3: the Science of Astronomy Ancient Greek scholars - Determined the approximate radius of the Earth (and knew the world was round well before the era of Columbus!) - Created a mathematical description of a geocentric model of the solar system. o Earth in the center of the universe, sun and planets orbit it. (wrong!) o Apparent retrograde motion was a problem for geocentric model. § Epicycles § Deferents o Lack of observable stellar parallax used as proof of the geocentric model and a stationary Earth. In truth, stars were just really, really far away! 3  Renaissance scholars - Nicholas Copernicus: created a mathematical description of a heliocentric model of the solar system o Sun in the center of the solar system, all of the planets orbit it. (correct!) o His model was crippled by the assumption of perfectly circular planetary orbits, making Copernicus’s model no more accurate at predicting planetary motion than the geocentric model of the ancient Greeks. - Tycho Brahe: precise naked-eye observations of the positions of the stars, planets, and moon. Provided crucial data used by… - Johannes Kepler o 3 Laws of planetary motion: § Planetary orbits are ellipses (not circles) with the sun at one focus § Planets sweep out equal areas in equal amounts of time § P2 = a3. (if P is measured in years and a is measured in AU) - Galileo Galilei o First to observe the night sky through a telescope. His observations more-or- less killed the geocentric model of the universe. § Shadows of mountains and valleys on the moon: heavenly objects are not perfect spheres. § Moons orbiting Jupiter: clearly objects in the sky can orbit something other than Earth! § Phases of Venus: should not be possible to see the phases in the geocentric model, yet expected in the heliocentric model. Science vs. Pseudoscience - The scientific method. - Law: a simple statement (usually presentable as an if-then statement) about some aspect of nature. - Theory: a well-tested set of models and laws that describe some aspect of nature. Typically form the basis of entire branches of science. 4  - Hallmarks of good science o Relies solely on natural causes o Progresses through the testing of models § Occam’s razor: the simplest model with the fewest assumptions is most often (but not always!) the correct one. o Models make testable predictions. If predictions don’t agree with observations, the model must be updated / edited or abandoned entirely. - Hallmarks of pseudoscience o Continues to make use of disproven hypotheses o Ignores evidence that disagrees with a hypothesis o Hypotheses that cannot be disproven through experiment or observation o Deliberate misuse of terminology o Deliberate misuse of statistics o Lack of peer review o Predictions are vague or exaggerated o Claims opponents to the hypothesis are part of a conspiracy o Lack of any progress (hypothesis never generates new predictions) o Preference for attacking dissenters rather than providing evidence. - Astronomy is a science. Astrology is a pseudoscience Coordinates on the celestial sphere - Right Ascension (RA): east/west position of a star. Measured in hours, minutes, and seconds. - Declination (Dec): north/south position of a star. Measured in degrees, arcminutes, and arcseconds. o Celestial equator: 0° declination o North celestial pole: 90° declination o South celestial pole: -90° declination - Origin (zero point) of the RA/Dec system = sun’s location on the celestial sphere during the March equinox. 5 Chapter 4: Making Sense of the Universe Scalars: have a magnitude and a unit - Mass (example: 5 kg) - Time (example: 12 seconds) - Speed (example: 15 m/s) Vectors: have magnitude, unit, and direction - Displacement (example: 9 miles to the west) - Velocity (example: 60 miles/hour to the right) - Acceleration (example: 10 m/s2 downward) Acceleration - Any change in velocity: speeding up, slowing down, or changing direction. - Acceleration caused by Earth’s gravity is about 10 m/s2 (pointing down). ALL objects accelerate at this rate as they fall. Newton’s laws: - 1st law of motion (the law of inertia): objects maintain a constant velocity unless acted upon by an outside force. - 2nd law of motion: F = ma - 3rd law of motion: for every force that acts on one object, an equal yet opposite reaction force is exerted upon another object. - Law of gravity: F = Gm1m2/r2 (that is, every mass gravitationally attracts every other mass, but the strength of the gravitational pull decreases as the distance between them grows). Misconception: there is no gravity in space - THE ABOVE IS A FALSE STATEMENT. - The fact that Earth’s gravity keeps the moon in orbit around us proves there is plenty of gravity in space! - Astronauts in orbit experience weightlessness because they are falling around the Earth, not due to a lack of gravity. 6  Tides - Caused by the moon’s gravitational pull being stronger on the near side of the Earth than the far side. - Spring tide: sun and moon work together to enhance the tides. - Neap tide: sun and moon work against each other to decrease the tides. Angular momentum - Conserved quantity for a spinning object. That is, momentum cannot be created or destroyed for an object, only transferred to/from another object. Chapter 5:Light and Matter Light has both particle-like and wave-like properties. Waves - Wavelength: distance from crest-to-crest or trough-to-trough. - Frequency: how many cycles (crest to trough to crest again) a wave goes through in a given time interval. Measured in hertz (Hz = 1/ second). - Wave speed = wavelength x frequency - Wave energy increases with higher frequency Electromagnetic spectrum - In order of increasing energy: radio waves, microwaves, infrared, visible, ultraviolet, x-rays, gamma-rays - Radio waves: low energy, low frequency, long wavelength - Gamma-rays: high energy, high frequency, short wavelength. - All of the above are forms of light; visible light is only special to humans because that’s the part of the spectrum we use to see. The speed of light is constant in vacuum and nothing can go faster than the speed of light in vacuum. In non-vacuum, light travels more slowly. Energy - Mass energy: the energy contained in physical objects. - Kinetic energy: the energy of motion 7  - Thermal energy: the energy of heat - Gravitational potential energy: the energy of objects lifted high above the ground. - Radiant (or radiative) energy: the energy of light - Energy is conserved: it can be transformed into other types or transferred to other objects, but the total amount of energy in the universe is constant. Wein’s law: hotter objects emit light with increasingly shorter wavelengths and higher frequencies (that is, hotter objects emit more blue light). Light / matter interactions - Emission (hot matter converts thermal energy into radiant energy) - Absorption (matter absorbs the radiant energy of light and heats up) - Transmission (light passes through matter, like a window) - Reflection (light “bounces off” of matter, like a mirror) Spectra - Spectra: split light into its individual wavelengths to create a rainbow band. - Spectra are created by devices such as prisms. - Types of spectra: o Continuous spectra: caused by a hot, dense object. o Emission spectra: caused by a hot gas o Absorption spectra: caused by the light from a hot, dense object passing through a cool gas. - Spectra tell us… o The chemical composition of an object. o Doppler Effect § Blueshift: object is moving toward us § Redshift: object is moving away from us § Spectral line broadening: object is rotating 8  Matter: - Atomic number: # of protons in an atom. Defines the element of the atom. - Atomic mass number: # of protons + neutrons in an element. Defines the isotope of the atom. - Just like light, matter has both wave-like and particle-like properties. Chapter 6: Telescopes Refraction: the bending of light as it passes from one material to another. Lenses: use refraction to gather light rays to a focal point - Human eyes are lens-based. They focus light to the retina. The pupil controls how much light is allowed to enter the eye and reach the retina. Basic properties of a telescope - Angular resolution: the ability to see fine detail. Better angular resolution allows smaller angles to be seen. Larger telescopes have better angular resolution. - Light gathering area: the ability to collect more light and therefore see fainter objects. Larger telescopes have better light gathering power. - Magnification: the ability to make an image appear larger than normal. Larger telescopes generally have better magnification, but the eyepiece lens (the part you actually look into) also plays a role. Telescopes are either refracting (lens-based) or reflecting (mirror-based). Good observing sites: - Dark (to minimize light pollution) - High (to minimize atmospheric blurring) - Calm (low winds also minimize atmospheric blurring) - Dry (to reduce cloud cover) Earth’s atmosphere vs. the EM spectrum - Radio, visible, the near-infrared, and the near-ultraviolet can pass through Earth’s atmosphere and reach the ground. Most of the infrared, most of the ultraviolet, 9  gamma-rays, microwaves, and x-rays are absorbed or scattered as they pass through Earth’s atmosphere; we need space telescopes to make observations at these wavelengths. Chapter 7: Our Planetary System and Chapter 8: Formation of the Solar System Major objects in the solar system - One star - 8 planets - 5 dwarf planets (at least) - 200+ moons - Millions of asteroids (estimated) - Trillions of comets (estimated) Patterns in the Solar System - Inner solar system: Mercury, Venus, Earth, Mars, and the asteroid belt o Smaller, rocky or metallic objects o Planets orbit the sun relatively close together - Outer solar system: Jupiter, Saturn, Uranus, Neptune, the Kuiper belt, and the Oort cloud o Larger, icy or gaseous objects o Planets orbit the sun increasingly far apart. - All of the planets orbit the sun in the same direction in which the sun spins. - Most of the planets rotate in the same direction in which the sun spins, although Venus rotates backwards and Uranus rotates “on its side”. - Most moons orbit their planets in the same direction their planet spins. o Retrograde motion: objects that orbit “the wrong way”. o Triton (the largest moon of Neptune) is an example of a retrograde moon. Catastrophic encounter hypothesis - Material was ripped loose from the sun by a close encounter with another star. This eventually formed the planets in orbit around it. 10  - Falsified: predicts very few planets in random, chaotic orbits around other stars, neither of which is true. Collapsing nebular theory - The solar system began as a nebula (gas cloud) that imploded. - Conservation of angular momentum will flatten the nebula into an accretion disk. Most of the nebula’s mass fell into the center to form the sun. Leftover mass formed the planets, asteroid belt, etc. - Process has been observed directly with other nebulae and young stars. - Frost line: hydrogen-based compounds like water (H2O) could only freeze into solids at a minimum distance from the sun. o Objects inside the frost line could only be made from rocky / metallic materials. o Objects beyond the frost line have rocky / metallic cores, but are covered in hydrogen-based ices. Particularly massive objects (the early gas giants) even attracted hydrogen / helium gas from the accretion disk, growing enormous hydrogen / helium atmospheres. The asteroid belt and the Kuiper belt were formed due to orbital resonances with Jupiter and Neptune respectively. Most impact craters were formed during the period of heavy bombardment early in the solar system’s history when left over debris from its formation were still common. Planetesimal: the early “seeds” that grew through collisions with other objects into the planets. Earth’s moon formed through the collision between Earth and a Mars-sized planetesimal. Chapter 9: Planetary Geology Inner planets in order of increasing distance from the sun: Mercury, Venus, Earth, and Mars. 11  Inner planets and Earth’s moon in order of increasing size: Earth’s moon, Mercury, Mars, Venus, and Earth. Planetary interiors: - Metallic core (densest materials) - Rocky mantle (mostly middle-density silicate rock) - Rocky crust (mostly lower density rocks) - Venus and Earth have mostly molten, convective mantles and liquid outer cores. Mercury, Mars, and Earth’s moon have cooled off more rapidly due to their smaller sizes and have more-or-less completely solid interiors. Chapter 10: Planetary Atmospheres Earth: mostly nitrogen and oxygen atmosphere Venus and Mars: mostly carbon dioxide atmosphere Mercury and Earth’s moon: no significant atmosphere Venus’s atmosphere is much thicker than Earths, while Mars’s is much more thin. Mercury Closest planet to the sun Oversized metallic core: outer layers of the planet may have been stripped away by a giant impact. Caloris basin: very large impact crater. The impact event caused earthquakes and warped terrain all the way on the far side of the planet. Highest temperature range of all of the planets. Locked in a 2-3 spin-orbital resonance. Most elliptical orbit of the 8 major planets; precession of the perihelion was a major proof of Einstein’s theory of relativity. Surface is heavily cratered, similar to the moon but lacking large maria. 12 Venus Second planet from the sun. Hottest of the planets. Extremely thick atmosphere for a rocky planet; atmosphere is the remnants of Venus’s evaporated oceans. - High amount of deuterium indicates the loss of an ocean’s worth of hydrogen. - CO2 atmosphere composed of oxygen (from what was originally water vapor) that bonded with carbon from surface rocks. Clouds composed of sulfuric acid. Many volcanoes, and the surface is mostly volcanic plains. Earth’s moon Maria: dark regions on the moon’s surface. - Large volcanic plains that fill in massive craters and low-elevation areas. - Darker than surrounding rock due to the high concentrations of iron. Ice in permanently shadowed craters at the poles (particularly south pole). Apollo 11: first mission to land humans on the moon’s surface. Members Neil Armstrong, Buzz Aldrin, and Michael Collins (last one stayed in orbit). Mars Fourth planet from the sun. Two small moons that are captured asteroids. One (Phobos) is slowly spiraling into the planet. Thin atmosphere occasionally blows up global dust storms. Ice caps much like Earth. A lot of evidence that water once flowed on the surface. - Planet cooled down, lost global magnetic field, and solar wind stripped most of the atmosphere away. - Oceans lost as a consequence of the above. 13  Many large geological features: Olympus Mons (volcano), Valles Marineris (canyon), and Hellas Basin (impact crater). Jupiter Most massive of the planets, arguably approaches the mass of the smallest stars. Great Red Spot is a 150-year-old (at least!) storm system similar to a hurricane. Four largest moons = Galilean Satellites (named for Galileo) - Io: extremely volcanic - Europa: may have a large subsurface ocean - Ganymede: largest moon in the solar system, larger than Mercury - Callisto: only Galilean moon not participating in an orbital resonance Saturn and Planetary Rings Titan: 2nd largest moon in the solar system, only moon with a thick atmosphere, only object other than Earth with surface liquids. Gaps in rings represent orbital resonances with moons in orbit around Saturn, or were a small moon is orbiting within the rings themselves. Uranus has the next most extensive ring system. Jupiter and Neptune also have them, but they’re must less obvious. Rings formed by… - Moons “shattering” after they pass the Roche limit - Enceladus and other, similar moons ejecting ices into orbit (cryovolcanism) Uranus and Neptune Near twins: both are blue “ice giants” with clouds of methane much bigger than Earth but much smaller than Jupiter and Saturn. Uranus: first planet to be discovered in modern times as opposed to being known for all of human history. 14  Neptune: discovered shortly after Uranus, when astronomers noted the orbit of Uranus indicated there must be an unknown massive object pulling on it. Great Dark Spots of Neptune similar to the Great Red Spot of Jupiter, but periodically fade away and then reform. Triton: largest moon of Neptune, only moon with a retrograde orbit, likely a captured Kuiper belt Object. Voyager 2 is the only space satellite to have ever gotten a close-up view of Uranus and Neptune. Ceres and the Asteroid Belt Main belt: between the orbits of Mars and Jupiter. Objects are mostly rock and metal. Ceres - Largest, most massive object (and only dwarf planet) in the asteroid belt. - Significantly smaller than Earth’s moon. - Once considered a planet before the rest of the asteroid belt was discovered. Asteroid belt is only crowded when compared to the rest of the solar system. Collisions are rare and all the asteroids combined have only a small fraction of the mass of Earth’s moon. Orbital resonances with Jupiter prevented a planet from forming and have cleared empty places in the belt. Pluto and the Kuiper Belt Icy analog of the asteroid belt beyond the orbit of Neptune. Objects in the Kuiper belt tend to be larger than asteroids for the same reason the gas giants are larger than the inner rocky planets. Four dwarf planets: Pluto, Eris, Makemake, and Haumea. Possibly many more. Plutinos: objects (including Pluto) trapped in a 2:3 orbital resonance with Neptune. This keeps Pluto from ever colliding with Neptune despite their orbits crossing. Pluto: five known moons, one of which (Charon) is fully half the size of Pluto itself. 15 Chapters 12 and 13: Comets and Extrasolar Planets Nucleus: solid icy body of a comet, Coma: gaseous envelope around the nucleus. Comets have a dusty tail + a second gaseous tail. Comets only have tails when they are close to the sun. Meteor showers occur when Earth passes through the orbit of a comet. Short period comets originate in the Kuiper belt, long period comets originate in the Oort cloud. Detecting extrasolar planets: o Direct imaging (can only be done for large planets in wide orbits around nearby stars). o Astrometry (watching the planet pull its star side-to-side as it orbits). o Doppler method (watching for blue/redshift of the star as the planet pulls on it). o Transit method (watching for the dimming of a star’s light when a planet passes directly in front of it) Types of planets most easily found with each of the above techniques? Extrasolar planets are common. Habitable zones – region around a star where Earth-sized planets can support liquid water on the surface. How brown dwarfs and rogue planets challenge the definition of a “planet”. Chapter 14: Our Star Hydrostatic equilibrium: gravity vs. thermal gas pressure Idea of nuclear fusion vs. nuclear fission The proton-proton chain (what is it, what it produces). Layers of the sun’s interior and each of their properties. Layers of the sun’s atmosphere and each of their properties Solar atmospheric activity due to magnetic fields 16  o Sunspots: how they relate to the solar cycle o Prominences / filaments, how they relate to sunspots o Solar flares and coronal mass ejections Differential rotation The solar cycle (time for a magnetic flip, how solar activity correlates, etc.) Chapter 15: Surveying Stars Wein’s Law Luminosity vs. apparent brightness Parallax o You do not need to reproduce the geometry used to define parallax, but you should be able to make use of the parallax equation. Units: parsecs, AU, light years. (know which is bigger / smaller) HR Diagram o Spectral sequence: O B A F G K M and how it relates to stellar temperature and spectral lines o Main sequence, giant, supergiant, and white dwarf stars on HR diagram. o Main sequence stars = on-going core fusion o Luminosity vs. temperature on the main sequence o Stellar radius vs. luminosity / temperature on the HR diagram. o What does the sun’s G2V designation mean? Distribution of stellar masses (how common are very massive stars, sun-like stars, etc. on a relative scale). Chapter 16: Star Birth Where do stars form? o In what regions of the galaxy? o In what regions of the ISM? The ISM is mostly hydrogen and helium gas, just like stars and gas giants. 17  Interstellar reddening due to dust in the ISM. Details of the collapse of a nebula into a protostar. o Massive clouds = many stars born in the same region at the same time o Protostars: what they look like, what is still different about them compared to main sequence stars. o Accretion disks and bipolar jets. Stellar winds and halting the addition of more mass onto a protostar. Hayashi tracks: movement of a developing star along the HR-diagram. Mass ranges of stars: what are the upper and lower limits? Chapter 17: Star Stuff Note: a better title for this chapter might be “stellar evolution” or “stellar aging”. Mass: the key parameter that determines how a star will change over time, how rapidly it will do so, and what type of object a star will become once it “dies” and all fusion processes stop. Red giant stars o What makes them so large? How do their sizes compare to other astronomical objects? o Are red giants more or less luminous than a main sequence star of comparable mass? o Are their surface temperatures hotter or cooler than a main sequence star of comparable mass? o What is happening to their cores? o What is the helium flash? What is a planetary nebula? Don’t let the name fool you! Fusion o What is the CNO cycle? o What is the triple-alpha process? o In what type of object does shell fusion occur? 18  o What is the heaviest element that core fusion can produce? How are heavier elements produced? o Helium capture and elemental abundances. What is a supernova? Chapter 18: the Bizarre Stellar Graveyard White dwarfs o Remnant, no-longer-fusing cores of lower mass stars. o Supported by electron degeneracy pressure o White dwarf supernovae § Chandrasekhar mass limit: 1.4 solar masses § How are they similar to high-mass star supernovae? How are they different? o Novae: what causes them? What objects must be present? o Be clear about the difference between novae and supernovae! Neutron stars o Remnant, no-longer-fusing cores of higher mass stars. o Supported by neutron degeneracy pressure o Pulsars § All pulsars are neutron stars, but not all neutron stars are pulsars! § How do we know pulsars must be a type of neutron star? § Pulsations due to rapid rotation and magnetic field. Black holes: o Remnants of the highest mass stars. o Singularity: a point of infinite density. o What is a black hole’s event horizon? How is it defined? o Observable properties of a black hole: mass, charge, and spin o Tidal forces rip apart an object that approaches too close to a black hole 19 Chapter 19: Our Galaxy Basic structure of the Milky Way: similarities and differences (gas content, rate of star formation, average stellar age, color, metallicities, orientation of stellar orbits, etc.) between three major regions. o Spiral disk o Central bulge o Outer halo Rough location of Earth in the Milky Way (are we in the bulge, disk, or halo?) Gas cycle in the Milky Way and other spiral galaxies. Ionization nebulae (aka H2 Regions) and reflection nebulae Formation of the Milky Way: similarities with the formation of the solar system. Super-massive black hole in the center of the Milky Way o Designated Sagittarius A* o Mass is greater than 4 million suns o Existence, mass proven by studying the orbits of near-by stars around it and (much more recently) direct imaging. Chapter 20: Galaxies History of the misconception of galaxies as “spiral nebulae” and why early astronomers didn’t know if they were part of the Milky Way or not. The Local Group: galaxy cluster to which the Milky Way belongs o Andromeda, Milky Way, Triangulum, and assorted dwarf galaxies. o Hierarchy of objects: § “Normal” galaxy: a few 100 billion stars or more § “Dwarf” galaxy: a few 100 million stars § Globular cluster: a few 100 thousand stars to a few million stars § Open cluster: a few 100 stars (up to the low thousands) o Milky Way / Andromeda future collision 20  Galaxy morphology and the Hubble tuning fork: know which types are gaseous, what their shapes look like, their overall colors, relative sizes, etc. o Spiral Galaxies § Barred Spirals (SB) § Unbarred Spirals (S) o Elliptical galaxies (E) o Lenticular galaxies (S0) o Irregular galaxies (Irr) The cosmic distance ladder: know the basic idea of the entire ladder (overlapping distance-measuring techniques, each depending on the one that came before for calibration), how each step is used, and the conceptual distances they cover (within the solar system? to near-by stars? to other galaxies?) o Radar ranging o Parallax o Main sequence fitting of star clusters (why were the Hyades important?) o Cepheid variable stars o White dwarf supernovae o Hubble’s law § How Hubble’s law indicates the universe is expanding. Universal expansion is what gives other galaxies their redshift What does this mean? (objects are not necessarily moving: the scaling factor of space itself is getting larger over time) § The Hubble constant vs. the age of the universe. Cosmological Horizon = a limitation due to the age of the universe and light travel time, not any “edge” of the universe. Chapter 21: Galaxy Evolution Lookback time: due to light-travel delay, the further away a star or galaxy is the further back in time we are seeing it. 21  Formation of spiral vs. elliptical galaxies: spin / density of protogalactic cloud. Galaxy collisions vs. irregular galaxies Starburst galaxies Active Galactic Nuclei (AGN) o Quasars vs. Seyfert galaxies: Seyferts = lower power, closer equivalents to Quasars. o Blazars (specific orientation: jet is along the line of sight) o Presence of accreting supermassive-black hole (just how massive are they? How do we know they exist?) o Relativistic jets: what causes them, how big are they compared to the main galaxy? Central Dominant galaxies: relative size, locations, morphology How the universe has changed over time: o Collisions less frequent o Irregular galaxies less common o Fewer AGN o All of the above due to galaxies being more spread out on average over time and therefore undergoing fewer interactions with each other. Chapter 22: the Birth of the Universe The Copernican principle: when viewing the universe, our point of view is in no way special. The cosmological principle: the laws of physics are the same everywhere o The universe is homogeneous (the same composition everywhere) o The universe is isotropic (the same distribution of matter everywhere) The Big Bang did not happen at any one point in space: all points in space were created during the Big Bang Cosmic Microwave Background (CMB) o “Afterglow” of the Big Bang 22  o Importance of thermal profile: proof the early universe really was hot as expected, and the redshift to microwaves was expected. o Early ionization of the universe vs. “First Light”: the CMB was emitted some time after the Big Bang event itself. Big Bang nucleosynthesis and particle creation o Production of early hydrogen during the big bang as energy became matter via E = mc2 o Generation of helium through universal fusion of hydrogen o Why fusion then ended until the development of the first stars Eras of the universe: o Planck era: the quantum-mechanical universe o GUT era: inflation occurred at the end of this era o Electroweak era: prediction of weak bosons confirmed by direct detection. o Particle era: generation of mass through particle creation o Era of Nucleosynthesis: universal fusion (see previous section) o Era of Nuclei: the ionized universe o Era of Atoms: the current era Evidence for the Big Bang: thermal profile of the CMB, relative abundance of H and He matches the theory’s predictions. Inflation: extremely rapid expansion of the early universe that explains several observations (such as the more-or-less uniform temperature and density of the universe on large scales and how the first galaxies formed). Chapter 23: Dark Matter, Dark Energy, and the Fate of the Universe Dark matter: unseen matter that seems to be much more common than “normal” matter. Evidence for the existence of dark matter: o Rotation rate of the Milky Way and other spiral galaxies. 23  o Dark matter and galaxy clusters: § Orbits of galaxies on the edges of galaxy clusters § Gravitational lensing Dark matter: WIMPs or MACHOs? o Weakly Interacting Massive Particles, a new form of matter that lacks an electric charge. o Massive, Compact Halo Objects: low-mass main sequence stars, black holes, and neutron stars that are hard to see from afar. The four fundamental forces and their basic characteristics: o Gravitation, Electromagnetism, Strong and Weak Nuclear forces o Quintessence: one of several hypothetical descriptions of dark energy Antimatter: mutual annihilation of matter and antimatter vs. pair production The fate of the universe: depends on the relative abundance of dark matter compared to the initial momentum of the Big Bang’s expansion. o Low abundance: recollapsing universe and a Big Crunch o Critical abundance: size of the universe eventually stabilizes. o Coasting universe: universe keeps expanding forever, ends in Big Freeze. o Accelerating universe: dark energy causes the expansion rate of the universe to increase over time. § Unexpected, but this is the universe we live in. § We don’t know what dark energy actually is yet. § Ends in either a Big Freeze (most likely) or a Big Rip (much less likely given current observations). § Evidence of acceleration: redshift of galaxies vs. distance Mass-energy budget of the universe: o The universe is 68% dark energy, 27% dark matter, 5% “normal matter” o 5% normal matter: split into 0.5% stars, 4.5% gas and dust 24