Introduction to the Universe
Introduction to the Universe ASTR 1000
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This 35 page Class Notes was uploaded by Adelia Adams on Monday October 12, 2015. The Class Notes belongs to ASTR 1000 at Georgia Southern University taught by James Higdon in Fall. Since its upload, it has received 14 views. For similar materials see /class/222011/astr-1000-georgia-southern-university in Astronomy at Georgia Southern University.
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Date Created: 10/12/15
Lecture 1 Overview Reminder Course Website httpcheller ph y georgiasouth em edujhigdon 1 Lecture 1 Overview Today Electromagnetic Radiation The Light Year A lightyear is the distance light travels in one year not a year with 50 fewer calories lOnelight year LY 951015 m ie 9500000000000000 m lAverage separation between stars is about 5LY 1 Lecture 1 Overview The Universe is big amp life is short Cassiopeia o Pegasus Warning We assume that physical laws in distant objects are the same ones we observe on Earth 9Unif0rmiljy of Nature 1 Lecture 1 Overview ElectraMagnetic Waves I Many examples of waves can be found in Nature ex Sound waves ocean waves seismic waves Properties of Waves Waveiengtn U n i Istu rbed Trough state Direction of wave motion 1 Wavelength OM distance between two creststroughs 2 Amplitude A how high wave is 3 Speed V how fast the wave moves 4 Period P time for passage of two creststroughs 5 Frequency f number of creststroughs that pass by in one second ie 20 per second 1 Lecture 1 Overview Properties of Waves 39opnlndure sures 9111 QABLI qloq 59111 g V SJamsuV 9 E lectro M agn etic Waves II o All charged particles modify space Electric field lines by creating an Electric Field E o This E eld extends through all space strongest near the charged particle 4 Field line gt e weakens the further away you are 2223 All charged particlesfeel the E elds of each other Szagggiry charged particles communicate electric forces this way Mt Vibrating vvave Charge 8 1 O 1 Lecture 1 Overview ElectraMagnetic Waves III Distant Vibrating Charge charge How fast are ElectraMagnetic waves Electromagnetic radiationwaves travel at the speed of light c 7 a W 39Hw 1 7 Lecture 1 Overview Light is an ElectraMagnetic Wave Wavaengm n m 40 Skin feels Eyes see Damages Damages thisng this range skin T39ssue Radio Infrared Vlsible Ultraviolet X ray Gamma ray l I 43 x10 7 5 x10 Frequency Hz The Earth s atmosphere 4 m 5 Atmaswmm 35an Some wavelengths of EA radiation pass through Earth s atmosphere eg optical amp radio 9Atm0sphere is transparent to these wavelengths Much of the W spectrum is absorbed by the atmosphere e g ozone other molecules This is a good thing 14 1 Lecture 1 Overview More on EM radiation Q What medium does EM use A Nothing 15 Energy content 0fEMradiati0n 1 Lecture 1 Overview Q amp A Time Consider two EManes A and B A has A 2000 nm while B has A 500 nm 1 Which EMane carries has more energy a A b B c same 2 By what factor a 025 b 2 c 4 d 8 1T 3 Which EMane could you see with your eyes a A b B c both 1 neither 1T Blackbody Radiation i Vibrating Wave Charge charge f u Hermit r quotquot Answer you collide them together 1 Lecture 1 Overview T emprature and Motion T100degrees T400 degrees 0 l 39 0 0 s 3 f0 0 4 8 V 5 u a v Temperature is a measure of average speed T 100 degrees T 400 degrees f O O s 390 Q 8 9 7 x3 395 1 EM spectrum and temperature 0 the resulting spectrum ofEliIradiation has a special shape Blackbody Radiation iiiten arty Fr queikv Note explaining the shape of this curve Blackbody curve was the rst success of quantum mechanics in the late 1890 s Max Planck won the Nobel prize for this 21 Blackbody curves and temperature Intensity arbitrary units Consider four Blackbodies with different temperatures but same size Visible spectrum Ha Ultraviolet 10 2 10 3 10 4 10 5 10 6 Frequency Hz 105 104 1000 100 10 Wavelengih nm 22 Lecture 1 Overview 1 Blackbody curves and temperature I There is a simple relationship between T and 9 of peak Visibie specmlm Ha Uitraviolet Wien s Law Intensity arbitrary units As T A man l l i I l 1014 10 10 10 5 10quotquot AS f Frequency Hz 7 peak 10 104 1000 100 10 Wavelength nm Temperatures using Wien s Law Infrared vrsrwe specmrm rvrrmwnrev Ha Frequency 62 x 1D Hz Wavelengm 43 um TSUK i l Frequency 52 x Hsz ma r Waueiangm 49 gun I T5CUK 1 i 1 106 Frequency 62 x mqu Wavelengm 450 nm T 6000 K Lecture 1 Overview 1 Lecture 1 Overview True 0f False 1 EM radiation can travel through a vacuum 2 Sound waves can travel through a vacuum 3 UV radiation has larger 9 than radio radiation 4 UV waves carry more energy than radio waves 5 Radiation from a star much cooler than the Sun will peak in the blue optical part of the spectrum M9 117 HG ampz 11 WMSMV Total energy from a Blackbody Visible spectrum Ha Ultravlolel l lnlensily al39bltrary umls 0 Frequency Hz 10 104 1000 100 10 Wavelenqlh nml Example Double the temperature EArea 9 24 2x2x2x2 16 times greater 1 The Doppler Effect Stars to enner 39da appear yawA V7 gt Direction ol motion Stars behind Stars in from appear a ear edshi ed bluashi ed o Doppler Effect 0 28 Lecture 1 Overview 1 Lecture 1 Overview The Doppler E ect Wave motion Observer behin sees Iongamhanmrmal wavelength rr WW Muv mg source HowA Prism Works Refraction Refraction is the bending of light as it passes from one medium air into another glass Key point light travels slighth slower in glass than it does in the air AAM 30 1 Lecture 1 Overview How A Prism Makes A Rainbow White light is a mixture of all visible wavelengths 31 A Simple Spectrograph White Light White light is a mixture of all visible wavelengths 32 1 Continuous Spectrum quotH 650 nm 500 nm 400 nm Sending Blackbody emission through a Spectrograph gives a continuous spectra 33 Hot gas in a glass tube Lecture 1 Overview 1 Emission Line Spectrum of Hydrogen Atoms HI Spectrograph i i i i i i i i usrv BOO 55H 45c JUU 150 SUU V JmJI hvngml mm Light comes out in a number of discrete wavelengths Emission Line Spectrum This pattern or spectrum is the same for any set of Hydrogen atoms 35 Each gas gives a distinct pattern of lines Lecture 1 Overview 7 Point 1 Neon lights are pretty 7 l m y H E 37 Magnesium 500 nm This is a spectrum Sodium 580 nm of a meteor Oxygen 800 nm 38 Lecture 1 Overview 1 Lecture 1 Overview Absorption Line Spectra What happens to Blackbody radiation passing through cool gas 600 um I 500 nm 6 400 nm You get a continuous spectrum from the 6000 K Blackbody except that light is absent at discrete wavelengths I The pattern of missing light depends on the gas between the source amp prism As if the gas absorbed the missing light 39 Emission amp Absorption Line Spectra It was noticed in the laboratory that for any given gas the A of the absorption lines matched the L of the emission lines For example here s the emission top and absorption bottom line spectra of Calcium 1 chellerphygeorgiasouthern eduNjhigdon Study guides are online Don t wait until the last second Trying to cram for a nal will result in a disaster Life in the Universe Are We Alone f4 Him ad jmfllfj j w WI U Where is Everybody Fermi s Paradox The Great Silence It is surprisingly hard to define life I Earliest fossilized life Bacteria cyanobacteria bluegreen algae go back 3 5 BYA It may seem surprising that bacteria can leave fossils but under certain conditions their thick cell walls can be replaced with minerals left this rock is Actually 3 billion years old It is composed of thousands oflayers of fossilized Cyano bacteria visable with microscope above Cyanobacteria fossils from Bitter Springs Chert Australia 2BY old Chemical Evolution Basic Idea Life evolved om non living molecules over time How reasonable is this idea Can it be tested a Haw Muunt Mmsu an a Indnnesm39s mm amvc volcanoes Lav mm mm this comes from chemical analysis of ancient rocks The Miller Urey Experiment Atmosphere mixture of methane ammonia hydrogen ampH2O Oceans 5 00cc ask lled with water Energy Input electrical discharge two tungsten electrodes simulated lightning discharges amp UV radiation from Sun Amino acids are the building blocks of all living things on Earth Every protein in your body is built around amino acids Amino acids form the basis of genetics DNA amp RNA use a 4letter alphabet of amino acids The Miller Urey Experiment quot r Even so is this the only way Life could arise Can there be other forms of Life We simply do not know How Common is Intelligent Life The Drake Equation number of technological intelligent civilizations now present in the Galaxy X The Drake Equation average rate of star number of fraction formation fraction of habitable Of those averaged gtlt stars having gtlt planets gtlt habitable over the planetary Within planets lifetime Of systems hose on which the Galaxy planetary life arises systems fraction fraction of those of those average life bearing intelligent lifetime of a planets gtlt life X technologically on which planets that competent intelligence develop civilization evolves technological society Intelligent Life in the Galaxy The Drake Equation is a series of estimates of factors that must be present for a longlasting technological civilization to arise Star systems 7 With planets With simple life With intelligence With technical society 7 With long lasting technology The Drake Equation SFR Average Rate of Star Formation in the Milky Way Mntell X fg alanetsx fhab X f al hab X flife X intell life X techno X Ltechno I The Drake Equation Fraction of Stars with Planets f planets Mntell X fplanetsX fhab X fgal hab X flife X intell life X techno X Ltechno I 0 X 075 Drake Equation Fraction of Planets that are Habitable fhabimble Something to consider About 50 of all stars are in binary or triple star systems eg a C en the nearest star to us is actually a triple star system Planets in multiple star systems can find themselves sometimes very close to a star or very close to a star leading to wide swings in temperature not conducive to li e Also planets can be ejected out of multiple star systems which is clearly bad for any developing life forms Life less likely to arise in binarytriple systems Drake Equation fhabimble continued Low mass stars have very small habitable zones low odds to nd planet within it Massive stars have very short lifetimes O amp B stars live N15million years then BANG M type F type star Gtype Nntell X fblanetsx fhab X f al hab X flife X intell life X techno X Ltechno 10 X 075X 01 Drake Equation Galactic Habitable Zone fgahab In addition there is a Galaxy wide habitable zone 7 High density and Sun s orbit intense radiation in here Galactic habitable zone Too few heavy elements out here Mntell X fblanetsx fhab X f al hab X flife X intell life X techno X Ltechno 10 X 075 X 01 X 075 Drake Equation Fraction of habitable planets that life actually arises on fhfe quotmm Mntell X fhlanelsx fhab X f al hab X flife X intell life X techno X Ltechm 10 X 075 X 01 X 075 X 10 Drake Equation Fraction of lifebearing planets where intelligence arisessfintel Mntell X fhlanelsx fhab X f al hab X flife X inlell life X techno X Ltechm 10 X 075 X 01 X 075 X 10 X 10 10 Drake Equation Fraction of intelligent societies that develop technology ftechno Mntell X fylanelsx fhab X f al hab X flife X inlell life X techno X Ltechno 10 X 075X 01 X 075 X 10 X 10 X 05 Drake Equation The average lifetime of a technologically advanced civilization Ltechno Mntell X fylanelsx fhab X f al hab X flife X inlell life X techno X Ltechno 10 X 075 X 01 X 075 X 10 X 10 X 05 X106 112000 intelligent technologically advanced civilizations in the Milky Way 11 Drake Equation Optimistic Viewpoint Note I didn t feel like adding 112 000 smileys to the above gure but you get the ideal Drake Equation Pessimistic Viewpoint The average lifetime of a technologically advanced civilization Ltechno Mntell X fplanetsX fhab X f al hab X flife X intell life X techno X Ltechno 10 X 075 X 01 X 075 X 10 X 10 X 05 X300 83 intelligent technologically advanced civilizations now in the Milky Way 12 Drake Equation Pessimistic Viewpoint Drake Equation UltraPessimistic Viewpoint Mntell X fplanetsX fhab X f al hab X flife X intell life X techno X Ltechno 10 X 075 X 01 X 075 X 01 X 01 X 05 X300 08 intelligent technologically advanced civilizations now in Milky Way This is a very possible explanation of both Fermi s Paradox and T he Great Silence We are alone 13 The Search for Extraterrestrial Intelligence The Search for Extraterrestrial Intelligence We are also communicating although not deliberately through radio waves emitted by broadcast stations These have a 24hour pattern as different broadcast areas rotate into view E Coastsse E coastlr s N Amer W Coast set N Amer W Coajsfrls Radio intensity Australia amp Japanrrise Australia set Japan set Distant observer Copyright 2005 Pearson Prentice Hall lnc 14 Sofar no detections But they ve just started 15
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