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Astro100 ExamIII Cheat Sheet

by: Jason Lepeska

Astro100 ExamIII Cheat Sheet Astronomy 100

Marketplace > University of Illinois > Astronomy > Astronomy 100 > Astro100 ExamIII Cheat Sheet
Jason Lepeska
U of I

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Cheat sheet to use on exam 3
Introduction to Astronomy
Bryan Dunne
Study Guide
50 ?




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This 1 page Study Guide was uploaded by Jason Lepeska on Wednesday July 20, 2016. The Study Guide belongs to Astronomy 100 at University of Illinois taught by Bryan Dunne in Spring 2016. Since its upload, it has received 17 views. For similar materials see Introduction to Astronomy in Astronomy at University of Illinois.

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Date Created: 07/20/16
THE MILKY WAY- ‣ Distant stars make a faint band of light circling the sky, a galaxy, milky circle, concentrated in strip Ne: kepler estimates 17% of bil stars are earth like William & Caroline Herschel counted stars in 683 different directions in the -Limitation of Doppler and transit methods: In edge on system: transits are possible,Dshift sky to measure the Galaxy, disk shape, Sun in center (problem)- didn’t take observed,radial velocity is stars true motion, planet mass dust into account: sim view and scatter blue light, making stars dimmer and obtained redder { infrared light let us see stars behind it} -Open clusters - loosely packed groups of several hundred to a few thousand In face on system: no transit, no Dshift stars - which are concentrated along the Milky Way. 5-17% of all stars are earth like, problem: high mass don’t live long -Globular clusters - dense balls of tens of thousand of stars or more (up to enough, low mass not habitable about a million stars) - which are widely scattered in the sky.  Harlow ASTROBIOLOGY 2 -Earths early geologic record is now gone, Shapley: controlled by gravitational field of entire star system-sun not center, -Heavy bombardment prevented any life center: Sagittarius & scorpius -Galaxy has 2 main components: disk: pancake shaped, stars and gas, sun in -Stromatolite: oldest fossils over 3 bil yrs old  created oxygen disk, 90% stars, young (hot, bright stars)+old, small and lil mass, lots of gas creating more complicated life, like us and dust,, orbit: same direction, nearly circular + sphere: galaxys halo and Timeline ‣ 4.4 billion years - early oceans form‣ 3.5 billion years - bulge,2%stars, old, red dwarfs(small, lil mass) and giants, lil gas and dust,, cyanobacteria start releasing oxygen.‣ 2.0 billion years - oxygen begins building up in atmosphere orbit: random, varying eccentricities (bulge: 10% stars, mixture of halo and ‣ 1 billion years - first macroscopic life‣ 540-500 million years - disk) Cambrian Evolution Explosion‣ 225-65 million years - dinosaurs and -milky way from above: see spiral arms-long curves of bright stars, see gas+dust small mammals (dinosaurs ruled) - Stars make new elements by fusion. Dying stars expel gas and new ‣ Few million years - earliest hominids (we are new-comers) elements,>hot bubbles (~106 K).>Hot gas cools> atomic hydrogen clouds Extremophiles-live in extreme environments , found in early life Amino acids in other places other than earth, from space (by meteorite form>cooling permits molecules to form>molecular clouds>Gravity forms new and comet) stars (and planets) in molecular clouds. Other life? Require liquid water, possible candidates: mars, some Jovian where?? – emission nebulae (H2 gas) only occur around hottest, blue, shortest lived (Otype), cold dusty gas clouds where star formation takes place, planets moon spiral arms(not solid body): waves of compression-trigger star formation,- -Mars: desert world, canali (dark features)-give belief of intelligent life rotate differentially- density wave, stars move in and doe when going out, on mars-thought to irrigate desert with water from ice caps,, mars was more hospitable to life…but too small, not enough internal heat, DON’T rotate-galaxy does, bright because: hot young massive stars, blue atmosphere escaped, planet froze -galaxy formation: The halo stars form within a turbulent proto-Galactic nebula -Europa: 6 Moon of Jupiter, new icy surface, Jupiter pushes and pulls as the gas clouds began to collapse under gravity>merged gas collapses> gas is slowly rotating, spinning disk> no more gas in halo>star formation ends the moon creating interior heat, liquid water under ice  geological >Spiral arms form, and organizes the star formation within the disk activity and deep ocean OTHER GALAXIES: 10,000 galaxies- expanded>100 billion galaxies -Titan-largest moon of Saturn, thick atmosphere BUT liquid ethane/methane seas on surface  great ethane sea,, it is geologically -Spiral: disk, spiral arms, gasrdnd dust, all ages stars, o/b type (barred spiral: active: volcano that spews mixture of methane + water ices, perhaps bar where arm comes off, 2/3 ,, ex: milky way) mixed with other hydrocarbons, has nutrients, energy and liquid for life -Elliptical: sphere no disk, lil gas and dust, yellow-red, few young, red giants dominate (largest-giant, smallest-dwarf) to evolve in -Irregular-chaotic no disk no sphere, blue-white, (o and B), rich in gas and dust Fi: evolution of intelligent life : evolution does not necessarily drive life -Rich Clusters- mostly elliptical, centrally concentrated, center has giant towards intelligence. Intelligence is not the goal of evolution, it is a train elliptical galaxies (evidence of galactic cannibalism) that fills a niche Fc: communication -Poor Clusters-many spirals, few elliptical, irregularly shaped, less crowded -agriculture, biggest breakthrough. 10,000 yrs ago-> writing and center (where we live-milky way and Andromeda galaxy) -Galaxies evolve by collision and merger, and interact, even those that don’t technology look like they do have in the past,, when they collide- too far apart to hit each L: Communicating Lifetime other, but gravity do interact>compress gas>star formation (starbursts) - Easy to envision 3 cases: [[ration of star size to star separation: typical distance between stars/typical 1. Communication eforts stop. Bored with lack of success or funding issues. star size ~ 50 million, rarely collide]] –collision shows that large elliptical are 2. Technological civilization collapses: exhaustion of resources and result of galaxy mergers (spiral can merge to make elliptical-major mergers population growth, detroy disks by tidal forces in collision) QUASARS: 3C 273-looks like a star but 2.4 bil light yrs away, super far but 3. Catastrophe! Nuclear war or various natural/astronomical problems. super luminous, tremendous energy output, change quickly (big things change Since we are talking long term, don’t forget the Earth only has 1-2 slower)-> tell us max size-> small size, centers of galaxies far away (young), billion years left before the Sun’s evolution kills of life. How long on average can an advanced civilization exist? usually disturbed by collisions ‣ Short Term (100-1000 yrs) Ex: m87, nucleus and jet- unusually luminous: active galactic nucleus (AGN)– - Give up on communication due to budgets. act like quasars -jet of plasma that emit radio waves shot out of AGN- moves nearly - Depletion of resources. speed of light - Population. Power source: NOT FUSION, energy by fusion, must fuse at least 10 Msun per - War. ‣ Long Term (100,000 to 5 Byrs– age of galaxy is ~13 Byrs and we took year, BUT by black holes: matter falls into black holes> energy converted into nearly half of that to evolve)- Stellar Evolution radiation (accretion disk>friction in disk turn into heat energy>produce thermal ASTROBIOLOGY 3 radiation (photons)) – evidence: motion of stars at center, find mass of 3 billion Msun,, speed of gas orbiting center Communicate with ET- radiowaves signal, not currently sending bcuz -Galactic center: star speeds up near center of mass, -stars orbit an objects that expensive is massive and small (supermassive black hole) -attempts- 1974 by the Arecibo telescope – series of on/off signals that could be rearranged into series -> colored ones-> image (problem: -collisionquasar normal galaxies [rich galaxies collide>material flow into sent to globular cluster-old star) black hole>quasar>gas used up>quasar fade to an AGN>galaxy retires as red -Failure of communication with ET- wrong frequencies, everyone + dead elliptical] – hint of milky way activity- from gamma ray results-recent activity from supermassive black hole-2 huge bubbles coming from center of listening but not broadcasting, we fail to recognize signal galaxy -Problems to overcome- space is big, Time (arguable do-able), Cost ________________________________________________________________________________ (trillion dollars) ____________________________ ASTROBIOLOGY 1: -Interstellar travel may never happen! -How long to colonize the Galaxy? -Find life titan/Europa?  Optimistic: every 500 years, colonization craft makes it to the next -universe: 100 bil galaxies>100 bil stars>planets>civilization, (if one per galaxy-) suitable solar system4mil yrs  Pessimistic-> 150 mil yrs The Fermi Paradox: where are the ET civilizations that must have developed earlier than we did **It is possible that ET intelligent life is abundant it our galaxy **if ETI is abundant, they would hv achieved a technological capability greater than ours- an advance civilization **With enough time, it is conceivably possible for a civilization to conduct interstellar exploration (self replicating Nano probes) **possible that ET has explored our region of galaxy (not pseudo science, but real logical consequences) **no reason to believe that it has or hasn’t happened  neither statements that earth has/hasn’t been visited by ETs has been validated – we just don’t know UFO phenomenon- sighting, abductions- all pseudo science (UFO- Unidentified Flying Object) "Extraordinary Claims Require Extraordinary Evidence" - Carl Sagan. R*: 10 stars/yr, -Problems—large number of sightings argues against alien space craft, -detecting planets: difficulty cuz of faint light source, direct imaging only space is so big, why would so many visit our earth constantly possible if planet is large and widely separated from parent star, and young (hot to emit intense infrared) Solutions to Fermi Paradox- 1) we are alone, 2)civilizations are common -Indirect technique: wobble/radial velocity but interstellar tavel is not, 3)there is galactic civilization and someday Wobbling stars-planets gravity tugs parent star, caused by planets orbiting we’ll meet them  no evidence that aliens hv visited stars-observed by Doppler effect. Star and planet each orbit around mutual center of mass [redshift: motion away from observer, wv longer,, blueshift: motion towards observer, wv shorter]=greater shift, greater speed…let us estimate mass of planet [Doppler shift: plot stars changing radial velocity over time)-tells us abt a planets mass (amplitude) and orbits radius(wobble


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