Stel Gal AstrCoReq ASTR 1211S
Stel Gal AstrCoReq ASTR 1211S ASTR 1020
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This 49 page Class Notes was uploaded by Dr. Deion Conroy on Monday October 12, 2015. The Class Notes belongs to ASTR 1020 at Georgia Southern University taught by Sarah Higdon in Fall. Since its upload, it has received 17 views. For similar materials see /class/222012/astr-1020-georgia-southern-university in Astronomy at Georgia Southern University.
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Date Created: 10/12/15
Lec 1 Prof Sarah Higdon Prof Sarah Higdon Of ce NIP 3019 next to elevator on the same oor as our lecture room Lectures ASTR1020 Tues ampThurs 12301345 W3001 Of ce Hours Thurs 1350 7 1450 pm Phone 478 5888 E mail g 39v 39 Web my 7 in i If you need to talk to me and I am not in my oi ce please Send me email 0139 see Ms Linda Smith in the Physics Main Of ce to schedule an appointment Lec 1 Prof Sarah Higdon Lee 1 Prof Sarah Higdon Who am I I GSU Astronomy Professor I PhD U Southampton England I ResearchProf positions I England Open University Rutherford Appleton Lab Queen MaryUniv of London I USA CalteohJPL Cornell I Research interests I Galaxy Formation I Interacting Galaxies I Interstellar Medium amp Star Lec 1 Prof Sarah Higdon What is Astronomy The science that seeks to determine properties and nature of stars planets galaxies etc everything beyond the Earth s atmosphere This includes their origin evolution amp fate Lec 1 Prof Sarah Higdon Lac 1 Prof Sarah Higdcm The most inclusive science Law Prof Sarah ngdun What is Astronomy eolo 3 The most inclusive science Law Prof Sarah ngdun chemistry What is Astronomy H MindMu an nu ma Dark clouds are rich in molecules Lec 1 Prof Sarah Higdon What is Astronomy Lec 1 Prof Sarah Higdon Some Fundamental Questions I How did everything in the Universe come into being 9 Chemical Elements Stars Galaxies I How is matter and energy distributed I What is the fate of the Universe I Do other planets support life I How abundant is life in the Universe Lec 1 Prof Sarah Higdon Lec 1 Prof Sarah Higdon Course Objectives I To learn astronomy I To better understand the nature of science I To gain perspective about ourselves and planet earth Lec 1 Prof Sarah Higdon 9 lli Outline of this Class This class will be divided into four roughly equal parts Part 1 Tools of Astronomy Nature of Light amp The Sun Part 2 Stars their birth life amp transfiguration Part 3 Galaxies Beyond the lVlilky Way Part 4 Quasars Active Galactic Nuclei Cosmology amp The Early Universe Lec 1 Prof Sarah Higdon 10 Lac 1 Prof Sarah Hl39gdon Course Structure Astr 1020 WebSite VERY IMPORTANT Lectures Tues amp Thurs Cover Essential course material quizzes Textbook Universe Stars amp Galaxies Roger Freedman amp William Kaufmann III Freeman Latest Edition Well written amp tied to lectures Lecl F39er Sarah Hgdun Course Structure Grades Quizzes 15 Cover material from previous lectures and homework Work in small groups No makeups Best 2 of 3 In Class Exams 60 multiple choice Worst exam will be dropped No makeup exams Missed exams will be graded 0 If you know you will not be able to take an exam for a valid reason you can make an appointment in advance of the test date to take a makeup exam All makeup exams will consist of essay questions Any exam missed for a valid reason must be reported to the instructor within two days of the exam Lecl F39er Sarah Hgdun Lec 1 Prof Sarah Higdon Course Structure Grades Comprehensive In Class Final 25 Mandatory you must attend this exam Same format as Inclass Exams Some comprehensive Questions but mainly from Part IV See Syllabus for time amp date 10 0 a mo Lsyllabushtml Lec 1 Prof Sarah Higdon Course Structure Grades All exams will be multiple choice using standard machine graded answer sheets Inclass quizzes cover lectures and assigned readingproblems a mixture of multichoice and inclass writing assignments Class attendance is not mandatory However it is in your best interest to attend Bring your student ID card number 2 pencil paper red ParSCORE 48TSM scantron Form No X 101864 PAR L course book and basic non programmable calculator to every lecture Lec 1 Prof Sarah Higdon Lec 1 Prof Sarah Higdon Please buy the correct scantron Red and narrow width ParSCORE 48TSM Form No X101864 PARL Note the idnumber has an extra column Always leave the last column blank amp write the number as well as filling in the bubblesl Lec 1 Prof Sarah Higdon 15 Grades amp Exam Schedule Grades A gt88 of possible points B 7587 C 6274 D 50 61 F lt49 L661 Prof Sarah Higdon 15 Lec 1 Prof Sarah Higdon Course Structure interruptions Please be considerate to39 your fellow classmates Snoring chomping slurping and chatting reading other class notes etc makes it hard for as to concentrate Lec 1 Prof Sarah Higdon Student Honor Lec 1 Prof Sarah Higdon Lec 1 Prof Sarah Higdon Reading Science books Science books cannot be read the same way you read novels poetry or newspapers heavy reading lots of info packed into each paragraph ideas are developed sequentially to understand paragraphB you need to understand paragraphA Suggestions 1 Read in a guiet place free of distractions eg library park 2 Read with a pencil in hand make notes in your own words of What you just read next to each paragraph 3 Read ACTIVELY After a paragraph ask yourself What did that paragraph say What was it about 4 Form a study group 7 talk over the end of chapter problems work on the study guide make mindm aps Lec 1 Prof Sarah Higdon Grade Prediction To be successful it is best to attend class Comprehensive In Class Final 25 Quizzes 15 In Class Exams 60 Worst exam will be dropped Bonus Talk 5 Final Grade Average Quiz 15 Average In class Exam 06 Final Exam 025 Bonus Talk Mark Lec 1 Prof Sarah Higdon Lec 1 Prof Sarah Higdon Final Grade Average Quiz 15 Average Inclass Exam 06 Final Exam 025 Bonus Talk Mark Assume you make the same grade in your final as your average inclass exam Perfect Score Quiz Average is 10 pts ie 100 In class Exam Average 100 Bonus talk is 5 out of 5 Fred grade 10015 100 6 100 25 5 105 A Change your predicted exam final grade to see how you can improve your overall score Lec 1 Prof Sarah Higdon Final Grade Average Quiz 15 Average Inclass Exam 06 Final Exam 025 Bonus Talk Mark Assume you make the same grade in your final as your average inclass exam 7 you haven t attended many lectures this semester Quiz average 10010857 030010 43 4310 43 Inclass Exams 70 75 60 gt Av inclass 725 Pred Grade 4315 7256 72525 0 645 4351812 0 68 C To make a B need 75 HARD ROUTE MAIGE IT UP ON THE FINAL Final 72525 18 need another 7 7568 187 25 Final Exam 25 F025 so F 25025 100 needed EASIER ROUTE do all the quizzes and give a talk and make a C in the nal exam but a B overall 10015 7256 72525 5 15 4351812 5 816 B Lec 1 Prof Sarah Higdon Lec 1 Prof Sarah Higdon Ask me about undergraduate I Lecl F39er Sarah Higdun Extra Credit Talks Thurs 426 and Tues 51 I This is an important bonus opportunity worth 5 points on your final grade Either on your own or in pairs prepare a 5 min presentation with an accompanying set of powerpoint slides You will give a presentation to the class I You will give me an electronic copy of your talk and a handout with two slides per page Including full references to any material used The printout does not have to be in color I Choose any ASTR1020 topic Points will be awarded for both style and content Make sure you give due credit to any material used in your talks Lecl F39er Sarah Higdun Lac 1 Prof Sarah Higdon Overview of Lecture 1 I Scientific method and scientific theories I Scientific notation powers often I Charting the heavens a flattened viewquot I Phases ofthe moon I The Seasons I Lunar and Solar eclipses I The speed of Light I Cosmic distances the light year beginnings of a 3D perspective Letl F39er Sarah ngdun i What Is Science Science is a technique for leaming about the physical Universe through the inteIplay of Theory and ExperimentsTests Prediction Letl F39er Sarah ngdun Lec 1 Prof Sarah Higdon What Is Science Science is a technique for learning about the physical Universe through the interplay of Th eory anal ExperimentsTests Ix Newton s Theory of Gra tY Scienti c Theory Must make precise predictions Must make testable predictions Must be framed in mathematics Occam s Razor Should be simple and elegant G M1 M2 d2 ExperimentsTests Can never prove a Theory in nite tests required A Theory can be disproved by failing one test Experimental results must be repeatable Lec 1 Prof Sarah Higdon 27 What Is Science A human endeavor sometimes blind alleys and Utums 9 people bring their own biases agendas 9 competition can bring out the best or worst in people Science Is Not A set ofbeliefs A collection of facts or numbers A nished product 9 Scienti c results are tentative Lec 1 Prof Sarah Higdon 28 Lec 1 Prof Sarah Hl39gdon Preliminaries Scienti c Notation A way to easily represent very big or very small numbers Onehundred 100 9 102 Onemillion 1000000 9 106 Threemillion 3000000000000 9 3 x1012 Onehundredth 1100 001 910392 Twohundredthousandth 2X1100000 000002 9 2 X 10395 Fivebillionths SKI1000000000 0000000005 9 5 X 10399 Mass of the Earth 59 x10 2 kg Mass of a student 60 x 101 kg Mass of an electron 91 x 10 1 kg Lem F39er Sarah ngdun 1 Objects visible in the night sky What do you see when you look up at the night sky Lem F39er Sarah ngdun Lee 1 Prof Sarah Higdon Objects visible in the night sky Stars N 3000 stars can be seen on a clear amp dark night by average eyesight 0 wide range in brightness 0 some brighten or dim 9 variable stars 0 stars have color red to blue 0 some stars are in physical pairs 9 binary stars ex Alchor ampMizar in Big Dipper Lec 1 Prof Sarah Higdon Constellations We often look for patterns Groupings of stars that are supposed to resemble animals mythical people or monsters Art is not science some can be Lec 1 Prof Sarah Higdon Lec 1 Prof Sarah Higdon The Milk Way Faint fuzzy band of light crossing the sky blank regions in MW MW is in fact our galaxy composed of 100billion stars called the Milky Way galaxy or sometimes The Galaxy blank regions are actually giant clouds of dust amp gas 9This is where stars form Lec 1 Prof Sarah Higdon Planets ve can be seen wo telescope Mercury Venus Mars Jupiter amp Saturn planets do not twinkle 9 stars do twinkle Venus can cast a shadow from Greek word for wanderer 9 their positions in sky change Lec 1 Prof Sarah Higdon Lec 1 Prof Sarah Higdon The Moon 39 EaIth s com ani n 9 always presents same s1de to Eanth Coincidence the moon mags nr Earth amp nnntakex a len gluten tfrnm covers same area of the 35 millian miles away in 1992 as it had m ani sky as the sun Lecl F39er Saran ngdon 35 The Celestial Sphere A Mommaalle MW I palm m quotmealstud i sum Flattened Perspective mwgm onstellations are groups of stars projected quotmquot W onto the celestial sphere I The celestial equator is de ned by extending the Earth s equator outward I The N amp S poles of the celestial sphere correspond to the Earth s poles Lecl F39er Saran ngdon Lec 1 Prof Sarah Higdon Can Use The Map of the Constellations to find other Galaxies eg The Andromeda Galaxy Easy to find observable with the unaided eye Pegasus Awingedhorse C assiop eia A queen of Ethiopia Andromeda Cassiopeia s daughter Lec 1 Prof Sarah Higdon 37 The Ecliptic I The ecliptic is the apparent path ofthe Sun amp planets through the sky I It is also the plane of the Earth s orbit about the Sun on the celestial sphere Note The ecliptic is tilted wrt the Earth s equatorial plane by 235quot North Celestial Pole A South Celestial Pole Lec 1 Prof Sarah Higdon 38 Lee 1 Prof Sarah Higdon Norm celestial pole Astronomical Coordinates I Equivalent to latitude and r decjm39 longitude on Earth quot I Declination Dec Degrees North or South of Equator ie 90 39 I Right Ascension RA Hrs quot Min Sec East of position of Sun at Vernal Equinox 0h23hr 59min 595ec Right Celestial ascensmn sphere Soulh celestial Lec 1 Prof Sarah Higdon pola In l Why the sky changes during the night Polaris The Earth rotates on its axis once per 24hours norm celestial not 0 Stars rise and set in the sky as a result unless close to pole quot 5395quot 0 Polaris lies close to the I may s Earth s rotation axis and 39 mm m so appears to moves the least 9 Polaris pinpoints North I Very important for early navigation Lec 1 Prof Sarah Higdon Lec 1 Prof Sarah Higdon Why the sky changes during the night Lec 1 Prof Sarah Higdon Apparent Motion of Stars at Different Latitudes B Atmidd39le northern latitudes b At the north pole c At Lheequakor Lec 1 Prof Sarah Higdon Lec 1 Prof Sarah Higdon Telescopes can have have AltAzimuth mounts Find star by converting RA and DEC to local Alt amp Az Zenith Altitude is Azimuth is measured from the horizon clockwise from a Altitude C g a a e a W North South amp 10 1180 Henge West270 I The zenith is the point on the celestial sphere that is directly above the observer Lec 1 Prof Sarah Higdon 7 u Meridian Zenith Stars near the end pole never set 399 Stars in the rar Polaris 50th are No 25 visible far only i I a short ume Celestial Pole North 39 t 7 West I The meridian is the great circle passing through the two poles of the celestial sphere and the observer s zenith Horizon Lec 1 Prof Sarah Higdon Lec 1 Prof Sarah Higdon The Earth spins on its axis and orbits the Sun the stars in the sky changes from night to night and follows a yearly cycle 9The starsconstellations you see on a Winter night are not the ones you see on a Summer night Constellations that the Sun moves through during the vear are called the sians of the zodiac path is ecliptic llations are Mes My 210 mm l the zodiac MW W I Nlu iL 39 39 Gm mm mm king 2quot mm whittzrl i cgnstellation quotWmv myquot Mm mums oes un appearin January June Dec 2 unnazl 39 Dec 4 a 21 gt4 1 a n may Ea 0W r limousines May2l Jul 2i Sabin Mam Apnzi WW Wm loroscopes state Aquarians born 0 A Earn39sapnmnmaslmmma NW 2 an 21 Feb 19 amquot 9 2 tut precession has changed Ocl 2t Smva is time that the gzaiglsuzv eushem quot3quot Seam W WLlulz unls inquotAquarius Lee 1 Prof Sarah Higdon 45 Precession rotation of Earth s axis itself makes one complete circle in about 26000 years Pole star changes POIariIS Vega pole star I current po 3 star Ln 3911000 Thuban M iquot pole star in I I I a 3000 BC l CD lquotr 233950 Earth s aXIs I of rotation 3 E uator Elip c a q plane 46 Lee 1 Prof Sarah Higdon Lec 1 Prof Sarah Higdon Lec 1 Prof Sarah Higdon I The Retrograde Wandering of Mars Mars appears to move East then loops West then loops back East Retrograde means backwards Earth orbits Sun faster than Mars does 9 Earth catches up to Mars and passes it From our vantage point Mars changes apparent position in sky relative to the distant stars Lec 1 Prof Sarah Higdon 1iWhy Are There Seasons on Earth Lec 1 Prof Sarah Higdon Tis the Tilt that Brings The Season The 5 Lhe umm unlslugh mifay r 5 S y TheSunxslowJ the mxdday wmter sky a The sun in summer Not to scale Lec 1 Prof Sarah Higdon 49 Summa I tar jolsllce una 21 90151ch Southern Dec 2 hamisphora V V Amurnnal equmox Sept2U Not to scale Womsvmvmmlm 50 Lec 1 Prof Sarah Higdon Lec 1 Prof Sarah Higdon 1 The Seasons Sun high in the sky in the summer and low in the winter Not to scale 51 Lec 1 Prof Sarah Higdon 211 Size 39 39Mmm39 360degrees circle mungulquot duamereruf 60arcmlnutes 1 degree mmu 60arcseconds 1 arominute 2 5 1 777777 7310323517 Why do stars twinkle and planets do not Lec 1 Prof Sarah Higdon Lac 1 Prof Sarah Higdcm of the Moon zsanysmu 4 wm g meaan 7 ght ughumm Sun In any nln mass l mu lab at manum Law Prof Sarah ngdun I Solar eclipses Cosmic coincidence The Sun and Moon have the same angular size Occasionally the Moon can pass between the Sun and Bath covering up the Sun in the sky This is OlaI Eph n e L251 me Sarah ngdun Lac 1 Prof Sarah Hl39gdon Three Kinds of Solar Eclipses Total eclipse 7 Moon completely covers Sun Partial eclipse 7 only pait ofthe Sun is hidde Latin wor 39 g tawngmmaas mm Plenth Hum Lunar eclipses Occasionally the Moon passes into the shadow cast by the Eanth L551 3er Sarah Higdun 56 Lec 1 Prof Sarah Higdon Lunar eclipses This picture shows the Moon entering the Earth s shadow at the start of a Lunar eclipse Note that the shadow is not straight but curved Ancient Greeks including Aristotle noticed that the Earth s shadow is round 9 Earth must be round Why is eclipsed portion of moon not dark 57 Lec 1 Prof Sarah Higdon How often can total solar eclipses occur Moon s orbit is 52 out of the Earth Sun plane tummy mquot l quot quot 9 Som etim es Moon s shadow quot quotquot misses Ea mm 9 Som etim es Earth s shadow 39 96 misses the Moon unvawame vm muse Umavmable my echusa Favovable m ecllpse Lec 1 Prof Sarah Higdon Lec 1 Prof Sarah Higdon The Speed of Light I Speed oflight 187500 milessec 675 million mileshr 9 678 X 108 mileshr 300000000 mSBC C I c is the ultimate speed limit Nothing can go faster than light as far as we can tell I The fastest way for information to get to us radio waves light ashes etc Lec 1 Prof Sarah Higdon Light Travel Times I Round the world in l7th sec not 80 days I EarthMoon 1 second I SunEarth 8 minutes I SunPluto 65 hours I SunAlpha Centauri 43 years I SunGal Center 35000 years I SunAndromeda Gal 2200000 years Lec 1 Prof Sarah Higdon Lecture 1 Overview Dr Sarah Higdon Of ce NIP 3019 next to elevator Lectures ASTR1020 Tues amp Thurs 123013 45 MP3001 Of ce Hours Thurs 1350 1450 Phone 478 5888 E mail 39 v quot Web 5 If you need to talk to me and I am not in my o ice please send me email or see his Linda Smith in the Physics Main Of ce to schedule an appointment Lecture 2 Dr S Higdon 2 Lecture 1 39 Overview Course Structure Astr 1020 WebSt I e VERY IMPORTANT Lectures Tues amp Thurs Cover Essential course material quizzes Textbook Universe Stars amp Galaxies Roger Freedman amp William Kaufmann III Freeman Well Written amp tied to lectures LemmeZDv 5 WWW Last Time I What is Astronomy What is Science I The night sky overview l Why the sky changes I During the night I From night to night I Eclipses I Seasons why is winter cold summer hot LemmeZDv 5 WWW Lecture 1 Overview Free Physics and Astronomy Tutoring Starts next week Math Lab opposite this Classroom 3000 in MathPhysics Building I MonTuesWedThur 5pm7pm Lecture 2 Dr S Higdon Today Electromagnetic Radiation Goals of this section 1 understand what EM radiation is amp how it transports energy across space 2 understand the di erent portions of the EM spectrum Xray ultraviolet optical infrared radio 3 understand how they are different 4 Blackbody radiation what it is and how it gives temperatures 5 Doppler Shift what it is and how it gives speed Lecture 2 Dr S Higdon Lecture 1 Overview 39 M 31 7the Andromeda galaxy 7 is the closest big spiral galaxy 0 it is 22million LY from us 22 x 106 LY lightspeed spaceship will take 22 x 106 years to get there as observed by us on Earth radio signals home will take another 22 x 106 years current spaceships are much slower than lightspeed Lecture 2 Dr S Higdon iHow do we learn anything at all 1 We use telescopes to collect faint electromagnetic EM radiation from distant objects in space 2 We use sensitive detectors 6 g CCDs to measure this faint EM radiation 3 We use laws of physics 7 as determined on the Earth 7 to interpret the EM radiation emitted by stars galaxies etc We assume that physical laws in distant objects are the same ones we observe on Earth So far testsobservations agree with the assumption of Uniformity of Nature Lecture 2 Dr S Higdon ElectroMagnetic Waves I I Many examples of waves can be found in Nature ex Sound waves ocean waves Waves on pond surface ripples are a simple example ripples caused by disturbance tossing rock in ripples waves move out in all directions at a certain speed ripples waves carry energy from site of disturbance 9 oating twig moves when the ripple reaches it Lecture 2 Dr S Higdon Properties of Waves Wavelength Uudlsturbed state Trough gt Dlremlon of Wave matron 1 Wavelength A 7 distance between two creststroughs 2 Amplitude A 7 how high wave is 3 Speed v 7 how fast the wave moves 4 Period 5 Frequency f 7 number of crests or troughs that pass by in one second eg 20 per second P 7 time for passage of two crests or two troughs Lecture 2 Dr S Higdon Lecture 1 Overview ijroperties 0f Waves x r i WaveA i i Wave B Which wave has the longest wavelength A or B Which wave has the highest frequency A or B Which wave has the smallest amplitude A or B LemmeZDv s ngdun ElectraMagnetic Waves II ll All charged particles modify space by creating an Electric Field E This E eld extends through all space strongest near the particle im 6 39 Weak away You are 35 All charged particles feelthe E elds of each 0 mum c arged particles communicate electric forces his w i What happens when you take one charge andj1ggle it mm mm W99 new LemmeZDv s ngdun Lecture 1 39 Overview Lecture 1 Overview iji lectroMagn etic Waves III liggling a charged particle sets up a ripple in the Electric field ie a traveling electric wave moving with the speed of light The distant charge will also start moving when the ripple in the E eld reaches it Distant Vibrating Charge charge Wave Amagnetic eld always accompanies the traveling electric wave 9 ElectraMagnetic Wave Lecture 2 Dr S Higdon 13 How fast are ElectroMagnetic waves Electromagnetic radiationwaves travel at the speed of light 7 c In a vacuum 0 187500 milessec 3 x 108 msec EMwaves travel slightly slower in gases And slower still in materials like glass Lecture 2 Dr S Higdon 14 Lecture 1 Overview Light is ElectraMagnetic Wave Reinvest Money In Vaults Until extras Grow Skin feels Eyes see Damages Da mages tilinge this range skin Tlssue Hadch Intrsred Visuals UmavIoIel X ray Gamma my I I 43 x10 75x 10 Frequency IHZI I I Wavelengm mm 700 400 1 nm 10399 m one billionth Lem 600 nm Speed of light 3 x 103 ms Abluemght 400 nm Lecture 2m 8 HIgdon 15 ummy mm mum 5n Is minus Lecture 2 Dr 8 HI Lecture 1 Overview The Earth s atmosphere Some wavelengths of EM radiation pass through Earth s atmosphere eg optical amp radio 9Atmosphere is transparent to these wavelengths Atmospher u lampqua span we Much of the EM spectrum is absorbed by the atmosphere eg ozone other molecules This is a good thing Lecture 2 Dr S Hrgdon 17 if Wavelike LightEM r adiati on can travel through the vacuum of space amp atrnosphere mostly water ever beemscuba divingsnorkeling 7 glass i esh X rays 85 gamma rays buildings radio waves Q What medium does EM use A Nothing Lecture 2 Dr S ngdon 18 Lecture 1 Overview Particlelike Energy of A Photon The energy of EMradiation is related to its frequency E h f Where h is a small number called Planck s Constant h 663 X 103934 Is Because frequency amp wavelength are simply related speed fX A we can also write the energy as Ehxspeed hc A T Energy is proportional to frequency If you increase f you increase E Energy is inversely proportional to wavelength Increasing A leads to a decrease in E LectureZDr S ngdon 19 QampA Time E hck Consider two EMwaves A and B A has A 500 nm while B has A 5000 nm 1 Which photon carries has more energy b c same 1T 2 By what factor a 01 b2 c5 d 10 3 Which photon could you see with your eyes a A b B c both d neither 1T Lecture 2 Dr S ngdon 20 Lecture 1 Overview How Sensitive are Radio Telescopes Compare the energy ofa falling snow ake to the energy ofa 21cm radio photon emitted from the Andromeda Galaxy Blackbody Radiation we want to connect EMradiation to bulk properties of a star galaxy or dust grain in space we know that jiggled electrons emit EMradiation frequency of the EM waves depend on how fast it is jiggled faster wiggle 9 higher frequency of EM how do electrons get jiggled or accelerated in Nature Answer One way is to collide them together LectuieZDi s Htgdun Temperature and Motion consider two boxes with gas particles one at 100 deg the other at 400 deg How are they different T 100 degrees T 400 degrees a a Q 9e 3 0 0 g 0 K 0 d 3 Q 1 Particles in hotter gas fly around faster on average 2 Some slowpokes in hotter gas there is a distribution of velocities 3 Collisions are at higher speed and more frequent in hotter gas Lecture 2 Dr s ngdon 23 Temperature is a measure of average speed T 100 degrees T 400 degrees 0 o Q to Q g 6 K d 3 Atomsmolecules in a gas that collide at higher speeds get their electrons jiggled more energetically The jiggled electrons emit EMwaves with greater energy ie EMwaves with higher frequency Collisions happen more often in hotter gas 9 more EMwaves Lecture 2 Dr s ngdon 24 Lecture 1 Overview Lecture 1 Overview EM spectrum and Temperature the resulting spectrum of EMradiation has a special shape Blackbadfv Radiation The shape re ects the average speed of colliding atomsmolecules It depends only on the temperature Density chemical composition etc not involved Nate explaining the shape of this curve Blackbady curve was thefirst success ofquantum mechanics in the late 189011 Max Planck won the Nobel prize for this LectuvezDv s ngun 25 Elckbody curves and temperature Consider four Blackbodies with different temperatures but same size Visible riecmxm A As temperature increases 1 emission peaks at smaller 7 emission peaks at higher f lnlmred Ul lmwulel 2 hotter Blackb odies emit more EM radiation per unit area at all 7 and all frequencies curves do NOT cross 3 shape of curve does not change at all my W V my Frequencv Hz In men Wavnteuqllv rm LectuvezDv s ngun 26 Lecture 1 Overview Wien s Law There is a simple relationship betweenT andk of peak 33quot Wien s Law A peak constant Constant 029 cm K 29 X10393 In K A peak 029am29 X10393 In T T AsTJ Aeag i AsTJfeak uhn Lectuvele s H gdun Temperatures using Wien s Law l mm mmquot in i E W Wang I Just Mam u m mum 13 Lectuvele s H gdun Wien s Law in Practice I What is the peak wavelength in Angstroms wavelength where Planck spectrum is at its peak that the Sun radiates at I Compare this wavelength to your peak wavelength assuming you are a perfect blackbody I What part ofthe EM spectrum do you radiate at Does the Sun radiate at LecluvezDv s Hludun ll Stephan s Law The Total Energy A Blackbody Radiates Example Double the temperature Flux VVm Z 9 24 2x2x2x2 16 times greater LecluvezDv s Hludun Lecture 1 Overview Lecture 1 Overview F 7 Stefan s Boltzmann s Law l I raise the temperature in the lament of a 100W light bulb by a factor 3 how many watts is it now radiating I This is equivalent to how many 100W bulbs Lecture 2 By S ngdun Bl F l Blackbody curve is an idealjz ation Lecluvele s Menuquot 32 r 7 Blackbody emission from stars amp cold dust in galaxies Galaxies are made up of 1011 stars 9 show TN6000 K Blackbody peak TM mm mum rm M on Intensitv LemuveZ Dy 5 WWW Astronomers Use The Kelvin Temperature Scale Astronomers use the Kelvin or Absolutti temperature scale 11mm madam Warn 7an Wm Bam M 273 C 0 C 100 C 0 K 273 K 373 K 9 Room temperature 300 K LeduveZ Dy 5 Hgan Lecture 1 Overview Lecture 1 Overview F u The Doppler Effect recall your experiences With passing retrucks With sirens or trains 9 siren s pitch goes up Le higher frequency as it approaches 9 siren s pitch goes down lower frequency as it moves away This39is the Daggler E ect the changing of pitch frequency Lie to motiim ofthesource EM radiation ie Light is also affected by the mum smwm Daggler EtZect aqu WEEK 39 7 Dlmnllnn nlnnllrn 1 Waves appear m u in p x reases a suuree yuu f fag LectuvezDv s Higan Lecture 1 Overview The Doppler Effect EM wave crests get bunchedup together when source moves towards you 9 blueshifted eguency goes 142 The faster the source moves the more they bunchup LEMMEZDV S Menuquot 37 True ofFalse 1 EM radiation can travel through a vacuum 2 Sound waves can travel through a vacuum 3 UVradiation has larger A than radio radiation 4 UVwaves carry more energy than radio waves meezov 3 Hum 38
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