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Astronomy Cheat Sheet (DRAFT) by

Final Review

This is a draft cheat sheet. It is a work in progress and is not finished yet.


How does critical density relate to universe?
⁃ Basically how much matter is there per cubic cm
⁃ If enough, enough gravity to recollpase
⁃ If not, Universe could go on expanding forever
⁃ Dark energy - seals the fate of the universe and an expansive body
⁃ Binary star: material could fall of companion onto pair star
⁃ doesn't fall straight in, spirals in and forms disk around the star
⁃ accretion disk ... holding pattern until it falls into star
Milky Way size
⁃ 100k light year across
How do we detect exosolar planets?
⁃ same as binary stars
⁃ direct detection: take a picture, hard because light gets swamped
⁃ transit method: if things are lined up, exoplanet will cross in front of star and block a portion of light (very tiny)
⁃ spectr­oscopic method: cross star, but doesn't block light
⁃ star wobbles a little bit due to the gravity of the star (doppler shift)
Cosmic module principal
⁃ the universe is the same every and in all direction (does not differ greatly anywhere)
⁃ helps explain the structure of the universe
⁃ made telescope obvs to measure positions of planets
⁃ first to say helioc­entric
⁃ mathem­atical laws for the orbits
⁃ used bra he's precise measur­ements
⁃ ellipses and speed change as they changed distant
⁃ telescopic discov­eries for keplar support
Spiral structure
⁃ spiral galaxies
⁃ waves of higher and lower density that travel through disk
⁃ higher density = spiral arms light up as stars form
Finding mass of a star
⁃ in binary = easy
⁃ in not binary = not easy
⁃ infer in comparison to other stars
Doppler effect
⁃ change in frequency or wavelength due to the relative motion of the source and observer
xray binary
⁃ exist and due to transfer of energy from of one star to next, X-ray flares

Still Everything

• baryonic and non baryonic WIMPS
⁃ baryonic sugges­tions are incomplete
⁃ baryons are what we are made of (all atoms)
⁃ non baryonic: things that are not made out of what we are made of (dark matter)
• cepheids
⁃ stage of the stars life after the main sequence
⁃ variable stars
⁃ They have very particular patterns of change and variab­ility
⁃ luminosity is related to the period
• pulsars and neutron stars
⁃ pulsars are neutron stars
⁃ connected by very strong magnetic fields
⁃ rotate very quickly
⁃ if you tried to take normal stars and spin them that fast, they would pull apart
⁃ radio waves are most common, optical light too and xray
• nova explosions and xray binary explosions
⁃ very similar
⁃ dump material onto surface of star = surface explosion
• young medium and old clusters when they turn off main sequence
⁃ for the sun, 10 billion years it turns on to main sequence
• Low mass
⁃ eject nebula, end up in white dawrf
• Galileo's experiment with velocity and accele­ration
⁃ rolled balls down a plain (demon­str­ation in class)
• Hubble relation explain age of universe
⁃ Several ways to think about it
⁃ universe is expansion, hubble relation tells rate of expansion
⁃ calculate how long ago expansion started which tells us distant
• Equili­brium in stars
⁃ Gravit­ational and Hydros­tatic equili­brium
⁃ acts like a gas or a fluid
⁃ Gravity tries to make the star contract
⁃ Pressure is center is trying to slow down contra­ction
• Era's of the Universe
⁃ First less than a second, particle era
⁃ particles are being created or destroyed
⁃ five minutes
⁃ nucleo­syn­thesis
⁃ first 400k years, when universe becomes transp­arent
⁃ radiation can flow freely throughout universe
⁃ after that, stars begin to form
⁃ cosmic microwave background
• Hubble relati­onship in graph form
⁃ Velocity x Distant
⁃ Straight line = hubble constant


• 1000 exoplanets
• Standard candle
⁃ object who's luminosity before you measure the distant
• Greenhouse effect
⁃ CO2 concen­tration in atmosphere increase, plants grow larger
⁃ Plant grows larger, removes CO2, puts out O2 = NEGATIVE FEEDBACK
⁃ Ice is a good reflector of sunlight, water is good absorber
⁃ Temper­ature of earth rises, ice melts, less reflected and more absorbed
⁃ warm the earth, melt more ice, make warmer = POSITIVE FEEDBACK
• Bootst­rapping
⁃ process of starting with one set of distance measur­ements and using it to progress
⁃ measuring parallax using radar inside solar system by using size of earth's orbit
⁃ once measured parallax, measure stars and clusters
• What is hubble constant?
⁃ 70 km/sec/Mpc
⁃ velocity for every km away from us, moving 70x that fast away from us
• Intera­ctions of light and matter in respect to radiation
⁃ light can scatter off of matter (blue sky)
⁃ absorb light (photons disappear)
⁃ produce light and photons (excite atoms in a gas)
⁃ bend light (refra­ction)
• Equili­brium of stars
⁃ amount of energy created = energy flowing out of star
⁃ have to stay in balance or star will heat up or cool down and mess up star
• Filaments (cluster of galaxies)
⁃ 3d spider web = filaments are lines and thread of web
⁃ basically where galaxies and stars are heavily concen­trated
• Wiens law / Greenhouse
⁃ wavelength at which most of the radiation comes out = temper­ature
⁃ our atmosphere absorbs infrared, radiation gets trapped but sun's radiation (sunlight) reaches the earth
⁃ earth heats up because infrared is being trapped
• Dark matter evidence
⁃ measured velocity of objects orbiting milky way
⁃ how much mass do you need/g­ravity to keep object in orbit
⁃ not enough present, has to be something else that has mass
⁃ gravit­ational lensing
⁃ light bends under influence of gravity
⁃ gravity distorts images more than there is present, must have dark matter
⁃ clusters of galaxies are filled with hot gas
⁃ why doesn't it escape? moving very fast
⁃ more gravity than should be present


• Dark energy existence
⁃ universe is accele­rating
⁃ shouldn't be accele­rating unless acted on by separate force
• Energy sources
⁃ Certain labs will help explain
⁃ Release gravit­ational energy to create heat
⁃ waterfall, gravity pulls water down which creates electrical energy
⁃ Chemical energy --> heat
⁃ burning
⁃ nuclear energy
⁃ nuclear reactions to create heat or kinetic
⁃ kinetic energy
⁃ motion energy
⁃ potential energy
⁃ springs
• Motions of spiral galaxy
⁃ motions in disk are orderly
⁃ motions in bulge are random and sponta­neous
• Measuring compos­ition
⁃ spectral lines
• Black holes and time
⁃ all clocks slow down when nearing a black hole
⁃ distorts time
• Black hole at the center of a galaxy
⁃ orbit of stars
⁃ something dark with TONS of mass at center
⁃ no light being emitted at center
• schwar­zchild radius
⁃ radius from which light cannot escape
• Olber's paradox
⁃ if universe is infinite in space and time, if i go out in a direction, i will eventually hit a bright star
⁃ sky should be bright, then
⁃ the universe is finite in time, i.e. BIG BANG
• matter vs antimatter
⁃ antimatter exists, we see it during nuclear reaction
⁃ counte­rpart to matter with opposite charges
⁃ very limited in nature
⁃ weird because in physics b/c antimatter and matter should be equal
• andromeda nebula?
⁃ didn't know it was a galaxy, classified as nebulae
⁃ hubble discovered that it was far away and as big as our Milky Way
• High Mass vs Low Mass
⁃ High mass ends in supernovae explosions
⁃ Low Mass turn into white dwarf
⁃ Binary stars can gain matter from other stars
• CDMS lab searches
⁃ One of the ways we look for dark matter
• Telescopes
⁃ size goes up, collecting area goes up^2
⁃ bigger telescope = better resolution