Astro 10B Study Guide rev. 2/24/2007
Astronomy 10B Study Guide – by Chapter
Know all of these points and you will do well
PROLOGUE (& THE GAS LAW)
What is Astronomy?
Scientific Study
Everything in the Universe – plus the Universe itself
Planets, stars, comets, galaxies, black holes, etc
Matter, energy, space and time
Origins are in Astrology – but Astronomy is a science; Astrology is not
Many astronomers really hate Astrology, but they have no sense of humor!
What is Science?
The purpose of science to produce explanations, models or theories
The scientific method (not the simplified one everyone knows)
Definitions of terms (e.g. theory, hypothesis, prediction, etc)
Philosophical underpinnings of science
Scientific Notation
The Gas Law (PV = nRT)
Almost all matter in the universe is the form of Gas or plasma
Definitions of pressure, volume, number, temperature, Kelvins, density
Playground analogy
The other version of the Gas Law, which is more useful to us: P = ρT
Equation of State tells us how a change in P or ρ changes the other
CHAPTER 1.
Night Sky – looks dome-shaped
Definition of terms (e.g. zenith and horizon)
Sky all rotates from East to West → Earth rotates opposite direction
Constellations
The Celestial Sphere
Definitions of terms (e.g. celestial equator, ecliptic, north celestial pole)
Coordinate system of the celestial sphere (RA & Dec)
North Star directly above Earth’s North pole + circumpolar stars
How does the North Star tell you your latitude?
Solar System View
Sun is at center of solar system
all planets orbit around in nearly a plane (which explains the ecliptic)
All planets orbit in the same direction (CCW as seen from NCP)
Most planets spin in the same direction (CCW as seen from NCP)
Astronomical Unit is the distance from the Earth = 9.3x108 mi (1.5x109km)
CHAPTER 2 – KEPLER’S & NEWTON’S LAWS (IMPORTANT!)
Kepler's laws (true for most all orbits – not just solar system)
K1: First law orbits are ellipses, w/ sun at one focus
definition of eccentricity, focus, etc (What’s eccentricity of Earth’s orbit?)
K2: Second law says planets sweep equal area in equal times
Planets speed up when in the part of the orbit nearest the Sun
K2 is equivalent to conservation of angular momentum
K3: Third law is the equation: P2 = k D3
Planets with bigger orbit size have much bigger orbital periods
Used to find mass of objects with satellites because k = 1/(m1 + m2)
Newton’s laws of motions
Definitions of velocity, speed, direction, mass, and acceleration
N1: Law of inertia - objects stay at constant velocity unless acted upon by a force
N2: F = ma
This gives us the definition of force – it is that which causes change in V
N3: Law of action-reaction
Normal version is confusing for our purposes
My version:
Forces act between 2 bodies, pulling them together or pushing them apart.
If an object is traveling in a perfectly circular path at a uniform speed is there
necessarily a force involved?
Newton's law of gravity: F = G M1 M2 / R2
Definition of terms: force, mass, distance, etc
Force of gravity increases when either mass increases
Force of gravity decreases when distance increases
Newton showed what relationship between the Moon and an apple?
Which falls faster a heavier object or a lighter one?
CHAPTER 3 - EARTH, MOON AND SKY
Reasons for the Seasons
The #1 wrong reason, changes in the Sun-Earth distance
Flawed because we’re closest to Sun in January
Flawed because seasons are flipped in N-S hemispheres
The right reason: tilt (it is more complicated but it is right)
The tilt changes the hours of sunlight over the course of a year (how?)
The tilt changes the angle the sunlight hits the ground (how spread out it is)
If you don’t know the reasons for the seasons, who was your astronomy instructor?
Phases of the Moon
Definitions (e.g. new, full, crescent, gibbous, waxing, waning and terminator)
Explanation for lunar phases (Sun illuminates it, we see it from dif angles)
Time of moonrise
depends on phase
50 minutes later each successive day
Solar eclipse happens only during New Moon, Lunar eclipse – Full Moon
Solar and Sidereal Days
Mean Solar Day is 24h and 361o
Sidereal Day is 23h56m and 360o
Explanation, Earth orbits Sun as it spins
Stars rise 4minute earlier each successive night
Winter and Summer constellations
Tides
Differences in the strength of gravity in near & far side – stretches planets, etc
Moon and Sun both cause tides
Spring tides and Neap tides
CHAPTER 4 – LIGHT, RADIATION AND SPECTRA
Electromagnetic Waves
Definitions (Electricity, Magnetism, wavelength, frequency, etc)
Electricity + Magnetism = Electromagnetism
E fields and M fields can cause waves EM waves (AKA light, EM radiation)
Equation: λf = c (if you know λ or f you can find the other)
The Electromagnetic Spectrum
They are all light: Radio, IR, Visible, UV, X-ray, Gamma-Ray
The only difference is light with different λ interacts w/ matter differently
Photons: packets of energy
E = fh
So Low E → low f → long λ
Cannot measure wavelike and particle-like properties of light at same time
Atomic Structure
Nucleus
Protons – number of which tells us which element it is
Neutrons – number of which tells us which isotope it is
Has almost all of the mass of an atom
Electron cloud
Electrons – number of which tells us the ionization state of the atom
Cloud is divided into orbitals – each with its own energy level
Atomic Spectral Lines
An electron has to have exact energy to inhabit an orbital
All transitions between orbitals require exact changes of energy
Each element only emits/absorbs photons w/ specific energies
We use these spectral lines to learn the composition of stars, etc
We use these lines w/ Doppler & Zeeman effects to learn other things, too
Types of Spectra
Bright Line Spectrum (Emission line spectrum)
Shows the atomic spectral lines bright
Comes from a gas
Continuous Spectrum
Shows all the colors of the rainbow, unbroken
Comes from solids, liquids and dense gases
We can measure temperature of objects with λmax • T = 3x106 nm•K
Dark Line Spectrum (Absorption line spectrum)
Atomic spectral lines dark, against continuous spectrum background
Comes from gases in front of solids, liquids or dense gases
Which spectrum does the Sun have? The Moon? A Neon sign? etc
Doppler Effect
It affects sound waves as well as light waves
If light source is coming toward you, wavelength, λ is reduced (blue shift)
If light source is going away from you, wavelength, λ is increased (red shift)
The amount of shift (Δλ) is proportional to the speed of the light source
Δλ/ λ = v/c
If moving at an angle (not directly toward or away) shift doesn’t give true speed
True speed is a combination of line-of-sight speed and tangential speed
To determine true speed we need to either:
Determine the angle somehow
Measure both LOS speed and tangential speed
Astro 10B Study Guide rev. 2/24/2007
CHAPTER 6 THE SUN – EARTH CONNECTION
Solar Composition
Hydrogen ~90%
Helium ~9%
All else ~1%
Solar Structure
The ‘Atmosphere’ of the Sun
Photosphere is surface – source of the light we see (6000K)
Above that: Chromosphere – Thin, almost transparent/pink (100,000K)
Above that: Corona – Very thin (non-dense) and very hot (1,000,000K)
Above that: The Solar Wind – blows out throughout solar system
The Solar Interior
Photosphere is surface
Below that is the Convective Zone – gets very hot and dense (varies)
Below that is the Radiative Zone – gets hotter and denser
Below that is the Core – extremely hot and dense
Nuclear fusion occurs here because > 12,000,000K
Solar Magnetism
The plasma moves along magnetic fields like beads on a string
Plasma cannot ‘cross’ magnetic fields lines
We measure magnetism using the Zeeman effect
Magnetic fields cause a number of phenomena
Sunspots – darker and cooler than regular photosphere
Plages – brighter, spider-web like things
Flares – X-ray explosions more powerful than 1,000,000 H-bombs
Can injure astronauts in space
Can damage spacecraft
Also release bursts of high speed electrons and protons
Coronal Mass Ejection’s (CME’s) – ejections of hot plasma
Sometimes they have magnetic fields
These mag fields can tangle with Earth’s causing blackouts
Often cause Aurora Borealis
Can damage spacecraft
Prominences – loops of magnetic fields sticking up from the Sun
We can see them because the stick off to the sides
We can see them because the hot plasma moves
The Solar Cycle
There is an 11-year cycle for magnetic activity on the Sun
All magnetic phenomena follow this cycle
We have observed this for ~400 years
By indirect means we can study it farther back
The Sun produces a tiny but extra energy when at a maximum
In mid 1600’s the solar cycle disappeared - Maunder Minimum
The Little Ice Age happened around the same time as this
There is still some debate whether the two are linked
CHAPTER 7 THE SUN – NUCLEAR ENERGY
Nuclear Fusion
The Proton-Proton chain
Three step process
The CNO cycle (not as important in the Sun, but important in bigger stars)
Six step process
Mass-Energy Conversion E = mc2
The Sun turns 4x106 tons of matter into Energy per second
The Sun turns 6x108 tons of Hydrogen into Helium per second
Energy Transport in the Sun
Radiative zone – a few 100,000 years
Convective zone – a few months
From Sun to Earth 500 seconds
Helioseismology (studying the Sun by looking at its sound waves)
Five minute oscillations – resonances of the Sun
Detect these sound waves by watching the photosphere bounce up & down
By comparing different resonant frequencies we can probe inside the Sun
Compare to embassy spying analogy
Helioseismology has taught us many things including these
Rotation of the solar interior
Temperature of solar interior
Deep within the Sun
just beneath sunspots
Motions of the plasma inside the Sun
Convection
Larger ‘rivers’ of plasma within the Sun
Astro 10B Study Guide rev. 2/24/2007
CHAPTER 8.SPECTRSOCOPY OF STARS
Brightness and Luminosity
Definitions of brightness and luminosity
the equation B = L/R2
Photometry – the measure of brightness
Star Colors and Spectral Types
Which color of star is hottest, which is coolest?
Which spectral type of star is hottest, which is coolest?
Which spectral type of stars is most ionized?
Which spectral type of stars has the most molecules?
If all stars contain Hydrogen why don’t we see H lines in ‘O’ type stars?
The spectral types (OBAFGKMLT) are in what order?
How were the letters originally assigned?
What are two ways to determine a star’s surface temperature?
Why can’t you use these techniques to determine a star’s core temperature?
Measuring Stars’ Properties
How do you measure the rotation rate of stars?
How do you measure the magnetic fields of stars?
What is ‘radial velocity’ and how do you measure it?
What is proper motion, and how do you measure it?
CHAPTER 9. MEASUREMENTS OF STARS (AND H-R DIAGRAM)
Distribution of Stars
Which are more common: low- or high- mass stars?
Which are more common: low- or high- temperature stars?
Which are more common: low- or high- luminosity stars?
Stellar Masses and Sizes
How do we measure the mass of stars? (we need two things)
What is the range of stellar masses possible?
What is the mass-luminosity equation? (approximate)
How do we measure the diameters of stars? (two ways)
H-R Diagram
What is the H-R Diagram (And why do we abbreviate it)?
What are the two axes of the H-R diagram?
Which side of the H-R diagram is hottest?
Which side of the H-R diagram is bluest?
Which side of the H-R diagram is most luminous?
Which corner of the H-R diagram has stars w/ the largest diameter?
Which corner of the H-R diagram has lowest mass main sequence stars?
Where on the H-R diagram do we find: White Dwarves, Red Giants, High-mass
Main Sequence Stars and Low-Mass M.S. Stars?
What is the main sequence?
Ninety percent of all stars fall where on the H-R diagram?
What are ‘binary stars’?
What are ‘spectroscopic binaries’?
What is the difference between a Star and a Brown Dwarf?
What spectral types are Brown Dwarves?
Which equation accompanies the H-R diagram? (Note: not in book)
If a star has a high luminosity and a low temperature what is its size?
Which stars are more massive ‘upper main sequence’ or ‘lower’?
CHAPTER 10: CELESTIAL DISTANCES
How do we know the size of the Earth (Hint: Eratosthenes)?
How do we know the Sun-Earth distance?
What is the Astronomical Unit?
How did we first measure the AU?
What is parallax?
Why is the parallax of stars so hard to measure?
What is a parsec and how is it defined?
What is a ‘standard candle’?
What is a Cepheid variable and why are they useful?
What is the period-luminosity relationship?
How can the H-R diagram help us measure the distance to a cluster of stars?
How do we measure the largest distances in space?
CHAPTER 11: THE INTERSTELLAR MEDIUM
What is the “interstellar medium”?
What is an HI region and how do we detect it?
What is an HII region and how do we detect it?
What is a Molecular Cloud and how do we detect it?
What is the Ultra Hot Gas and how do we detect it?
What is the temperature and density of a HI region?
What is the temperature and density of a HII region?
What is the temperature and density of a Molecular. Cloud?
What is the temperature and density of the Ultra Hot Gas?
How are Molecules and Dust inter-related?
What is ‘interstellar extinction’?
What is ‘reddening’?
Why does dust block visible light better than radio waves?
CHAPTER 12: STAR FORMATION
From what type of ISM do stars form?
Why is it so difficult to observe star formation?
Which stage of star formation occurs first?
What are the stages of star formation?
What is a ‘proto-star’?
What is the main difference between a proto-star and a main sequence star?
What is stellar wind, and when does it begin?
What determines the rate of star formation (and stellar evolution)?
Planets form from what part?
How does the H-R diagram help us understand star formation?
How do we learn about star cluster formation with the H-R diagram?
CHAPTER 13: STELLAR EVOLUTION
Why do stars spend most of the time on the main sequence (M.S.)?
Which spectral type of star spend the most time on the M.S.
What is the equation for mass vs. life expectancy of stars? (approx.)
What is a Red Giant?
What causes stars to turn into Red Giants?
Where are Red Giants on the H-R diagram?
What happens to a star’s core when it runs low on Hydrogen?
Then what happens to the shell of Hydrogen around the core?
What does the inner core start ‘burning’ at 100 million K?
What happens if the star has very low mass?
After the inner core runs low on Helium what happens to it?
What happens to the shell of fresh Helium around it?
What happens to the Carbon core of low-mass stars ( < 7Mo)
What’s the difference between the He flash and the He conflagration?
Which types of stars experience the Helium flash?
Stars over what mass can convert Carbon into heavier elements?
What’s the heaviest element whose production gives off energy?
What happens when a Star’s core is made out of that element?
What are the stages of evolution for a low-mass star?
What are the stages of evolution for a high-mass star?
Which stages of evolution will the Sun go through?
How can the H-R diagram tell you the age of a cluster of stars?
Why are there sometimes 2 ‘branches’ on the H-R diagram for star clusters?
What is the upper branch called?
CHAPTER 14 WHITE DWARF & NEUTRON STARS
What type of stellar corpse will the Sun leave behind?
What type of stellar corpse would a 20M~ star leave behind?
What is the upper limit for the mass of a White Dwarf?
What is a typical size of a White Dwarf?
What is the typical density of a White Dwarf?
What is the upper limit for the mass of a Neutron Star?
What is a typical size of a Neutron Star?
What is the typical density of a Neutron Star?
What is electron degeneracy?
What is neutron degeneracy?
How much mass does a star lose by time it becomes a White Dwarf?
What is a supernova?
What causes the supernova?
How much energy does a supernova give off?
What fraction of supernova energy is light, neutrinos, other?
Why is Iron the heaviest element made by stars (aside from supernovas)?
How are elements heavier than Iron produced?
What is a Pulsar?
What is the lighthouse model of Pulsars?
Why can’t we see all Pulsars (even if they are close by)?
Who discovered Pulsars but was betrayed by her advisor?
How big of asshole was he?
What is a recurring Nova?
How can binary star systems produce a special type of supernova?
Astro 10B Study Guide rev. 2/24/2007
CHAPTER 15 BLACK HOLES & GENERAL RELATIVITY (G.R.)
What does “relativity” mean?
What is classical (or Galilean) relativity?
What is special relativity?
What observation is it based on?
What are some tests of special relativity?
What test of G.R. involved the ground floor and top floor of a building?
What is general relativity?
What is the equivalence principle?
What is gravity according to general relativity?
What causes spacetime to curve/warp?
How do you make it curve/warp more?
What travels in straight lines in spacetime?
Why does the equivalence principle imply warping of spacetime?
What is a black hole in the classical sense? (hint: escape velocity)
What is a black hole according to general relativity?
What is the event horizon?
What is the Schwarzschild radius?
What would happen if the Sun were replaced by a 1M~ black hole?
How big would a 1 M~ black hole be?
How does the Schwarzschild radius vary with a black hole’s mass?
How do we detected black holes if we cannot see them?
Why would jumping into a black hole be suicide?
Why aren’t black holes ‘cosmic vacuum cleaners’?
Why is light from a Black Hole red-shifted?
Is the light from the Sun red-shifted for the same reason?
CHAPTER 16 THE MILKY WAY GALAXY
What are the three main parts of the Milky Way?
What are the dimensions and mass of the disk? (both parts)
What are the dimensions and mass of the nuclear bulge?
What are the dimensions and mass of the Halo? (both parts)
What part of the Milky Way has the highest % young stars?
What part of the Milky Way has the lowest % young stars?
What part of the Milky Way has the most metal-rich stars?
What part of the Milky Way has the fewest metal-rich stars?
What part of the Milky Way has the most dark matter?
Where is the Sun located within the Milky Way?
How long does the Sun take to orbit the Milky Way?
How do we determine the mass of the Milky Way? (two ways)
How do we observe the far side of the Milky Way?
How do we observe the Halo of the Milky Way?
How do we determine the rate stars orbit the Milky Way?
How did we discover that there was dark matter in the Milky Way?
How did we measure the amount of dark matter in the Milky Way?
What fraction of the Milky Way is dark matter & where is it?
What explanations have been offered to explain the dark matter?
What is wrong with those explanation?
Where is the 3,000,000 M~ Black Hole?
CHAPTER 17 TYPES OF GALAXIES
Which type of galaxy is the Milky Way?
Which type of galaxy has the fewest supernovas?
Which type(s) of galaxy has gas and dust; which don’t?
What color are the different types of galaxies?
What is the mass-to-light ratio for each type of galaxy?
Why do the colors and mass-to-light rations differ?
The smallest galaxies are which type?
The largest galaxies are which type?
What causes spiral arms?
Why are some galaxies irregular?
How do we measure distances to galaxies?
Do spiral galaxies and elliptical galaxies evolve into each other?
What is the Hubble Law equation?
If a galaxy moves away twice as fast – how far away is it?
What observation about distant galaxies lead to the Hubble Law?
The Hubble constant is equal to 1/________?
If the Hubble constant is 20 km/s/Mly , what’s the age of the Universe?
Does the Hubble law say we're at the center of the Universe?
Would other galaxies observe the Hubble law, too?
Is spacetime expanding or is the matter just flying apart?
CHAPTER 18 AGN’S, QUASARS
What do Astronomers call Quasars?
Why are Quasars called “quasi Stellar objects” (QSO)?
If a QSO is a AGN, what are TLA's?
What is the typical luminosity of a quasar?
Why do we think quasars are compact objects?
What’s the suspected energy source for a quasar?
Most quasars appeared when the universe how old?
How do we explain this?
Are Quasars are a type of Active Galactic Nuclei?
Does the Milky Way have a quasar at its center?
Are quasars are among the most distant objects we can detect?
Are quasars the most red shifted objects we can detect?
Does this mean Quasars are among the oldest objects we can see, why?
What is a Seyfert galaxy?
What is an active radio galaxy?
What are the jets which come out of active radio galaxies and quasars?
CHAPTER 19 GALAXIES, CLUSTERS AND LARGE SCALE STRUCTURE
What is the ‘cosmological principle’?
What does ‘isotropically’ mean?
How do we think giant elliptical galaxies form?
What are the ‘great voids’?
Which is larger: the Local Group or the Local Cluster?
How are galaxies, groups and clusters distributed through space?
Which type of clusters contain the most giant elliptical galaxies?
Where would you find a galaxy which is the result of several mergers?
What happens when galaxies collide?
How would you explain a galaxy having multiple nuclei?
Why do distant spiral galaxies have more blue stars than nearby ones?
According to bottom-up formation, which structures formed first?
Where have astronomers found evidence for dark matter?
Why do we look ‘back in time’ when we look at distant galaxies?
What are MACHO’s?
What are WIMP’s?
How has star formation changed compared with 8 Byrs ago?
CHAPTER 20. THE BIG BANG AND EARLY UNIVERSE
Einstein's cosmological constant was:
The cosmological constant is equivalent to what discovery?
What is the explanation for the expansion of the universe?
Which observables does the traditional big bang theory explain?
Where did the Big Bang occur?
What observation could the original Big Bang theory not explain?
Which period of the Big Bang occurred earliest?
Which is expanding: the distance between galaxies or spacetime?
At which temperature do all the rules break down?
At which temperature did protons form?
At which temperature did electrons form?
Why aren't new protons and electrons forming today (s as they did during the big
bang)?
Which took longer: the formation of protons and electrons, or the formation of
galaxies from protons and electrons?
At what temperature did the universe become transparent?
Who discovered the Cosmic Background radiation (CBR)?
The Cosmic Background Radiation is observed in which band?
When we look at the CBR, we see remains from
The CBR spectrum corresponds to which temperature?
Which temperature was it when it was emitted?
The small variations in the CBR match what distribution?
Grand unified theories are about
Which forces unify at the lowest temperature?
Which forces were unified a hundred years ago (or scientists realized two forces
were one and the same at that time)?
Explain the inflationary universe model
How could the universe inflate faster than the speed of light?
How does quantum mechanics affect the distribution of matter in the universe?
How does inflation explain the matter-anti-matter imbalance?
How does inflation explain the density of the universe?
Explain GUTs
What is the last enduring problem with GUTs?
Which observations can GUTs and inflation explain?
About what fraction of the universe is dark matter?
About what fraction of the universe is normal matter?
About what fraction of the universe is dark energy?
Dark energy is responsible for
Dark energy is opposite to which force?
Dark energy is similar to which constant?
Dark energy tells us that the universe will collapse, when?
How was Dark matter detected?