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Date Created: 09/19/15
Origin of the Asteroids 0 Solar Wind Cleared leftover gas but not planetesimals 0 Whatever didn39t go into planets formed asteroids 0 Most inhabit asteroid belt between Mars amp Jupiter Jupiter s gravity prevented a planet from forming there Formation of the Moon Giant Impact Theory Earth collided With Matssized planetesimal Ejected part of Earth s mantle Coalesced into Moon 7 Orbits same direction as Earth rotates 7 ower density than Earth 7 Earth was spun upquot Radiometric Dating Unstable isotopes are I Potassium A9 4 quot radioactive D 075 7 Q 9 Change 111to another 8 V 5 050 ThaiHifs C 1sotope through g LE t radioactive decay 0 25 x 0125 3 bah was half life is time for 1 I i i o o 1 2 3 i 4 5 half to decay 125 7 375 time since rock formed billions of years Measuring relative amounts of two isotopes amp knowing half life of radioactive isotope gives age of rock Q l a fraction of sotope 0 U1 0 Potassiumr40 Argon740 ThaHrhfe 2 hawWes 3 halfWes l 1 2 3 5 1 25 9 3 3 75 me since rock formed bilhons of years Sample question A meteor is found to contain 3 times as many Argon 4O atoms as Potassium 4O atoms Given that Potassium 4O has a half life of 125 BY about What is the age since the meteor was last melted The Age of our Solar System Radiometric dating measures age since rock was solid On Earth geology causes rock to melt and resolidify gt Earth rocks can t tell us Solar System s age Use rocks that have not melted or vaporized since they condensed from the Solar nebula meteorites imply an age of 46 billion years for Solar System Radioactive isotopes are formed in stars amp supernovae suggests that Solar System formation was triggered by supernova short half lives suggest the supernova was nearby Extrasolar Planets Shouldn t other stars have them as well Planets orbiting other stars called extrasolar planets 0 Long assumed to exist e g in sci 0 But direct evidence rst came in mid 90 s Planet discovered to orbit star 5 Pegasi Now have detected over 200 extrasolar planets Detecting Extrasolar Planets Can t actually make images of extrasolar planets Angle between star and its planets too small to resolve Planets only re ect light so too much glare from star Detecting Extrasolar Planets 0 So we detect planets indirectly by observing the star 0 Planet gravitationally tugs the star causing it to wobble 0 This periodic wobble measured from Doppler Shift of star s spectrum Slalml rhits rm to scam Use Doppler shift to detect tiny wobble of star duento planet To Eanh 100 Orbital Radius All 9 5 ane as m e 5 05 Time ast 1m quotwas Cream 0 Plot of the radial velocity VS time forms a wave Amp amp period gt size amp period of planet s orbit From Kepler39s laws can infer mass planet Measuring the Properties of Extrasolar Planets 0 Doppler technique gives planet mass and orbit 0 If Planet transits star can also infer its size planet from amount of starlight it blocks Planmary Transits To see transit must View along plane of planet s 01bit transits are relatively rare Allow us to calculate density of planet most extrasolar planets detected have Jovianlike densities 5173 mm brightness ear to be L ian than ou quot tern closer to their stars Orbits are closer and more elliptical 4 mm nlJumlev msra c lrrvnbmp ul y v r r v v w u lllllv1 lrllll n 2 L 74 7 dislmce lmm sin m a 2 a DlS GHCe mm mm AU Implications for the Nebular Theory 0 Extrasolar systems have Jovian planets orbiting close to their stars Theory predicts Jovian planets form in cold outer regions 0 Many extrasolar planets have highly eccentric orbits Theory predicts planets should have nearly circular orbits 0 Is the nebular theory wrong Not necessarily it may just be incomplete Perhaps planets form far from star and ljfililgff llle towards it Doppler Cotillnicne towards nding close Jovian planets Are they the exception or the rule Migrating J ovians could prevent terrestrials from forming Is our Solar Solar System Photometry of the Pleiades Name Student Data Sheets 1 The Earth rotates to the and the stars drift to the 2 Sky Readings Filter Mean Sky Countssec U B V 3 Possible Red Giant Stars Star Nunber RA IEC 4 Consider the star near RA 3 h 44 m and Dec 24 35 It seems curiously out of place with respect to the main sequence What type of star might this be Upon what did you base your decision Photometry of the Pleiades Name Student Data Sheets gar hr sec deg sec BV 1 3 41 05 24 05 11 2 3 42 15 24 19 57 3 3 42 33 24 18 55 4 3 42 41 24 28 22 5 3 43 08 24 42 47 6 3 43 08 25 I 46 7 3 43 39 23 28 58 8 3 43 42 23 Z 34 9 3 43 56 23 25 46 10 3 44 03 24 25 54 11 3 44 11 24 07 23 12 3 44 19 24 14 16 13 3 44 27 23 57 57 14 3 44 39 23 27 17 15 3 44 39 24 34 47 16 3 44 45 23 24 52 17 3 45 09 24 50 59 18 3 45 27 23 17 57 19 3 45 28 23 53 41 20 3 45 33 24 12 59 21 3 46 26 23 41 11 22 3 46 26 23 49 58 23 3 46 57 24 04 51 24 3 47 29 24 Z 34 Photometry of the Pleiades Name Student Data Sheets 5 Using the distance modulus equation 1 10 X 10639ng5 in the Introduction to calculate the distance to the cluster in parsecs Then convert your answer to light years Show all work in the space provided Distance to cluster parsecs Distance to cluster light years In January 2004 astronomers from CalTech and NASAJPL using interferometry calculated the distance to this cluster is between 434 and 446 lightyears 6 As a percentage how does your calculated value compare to 440 LY SHOW YOUR WORK Photometry of the Pleiades Name Student Data Sheets Take Home problem Using only your graphs and resulm calculate the apparent magnitude of the Sun if it were located in the Pleiades cluster Explain your procedure in a narrative and show all your math HINT You ll need the absolute magnitude ofthe Sun The Sun is a type G2 star with a BV ofabout 062 Now you can use the clear plastic graph to estimate its absolute magnitude For next class on Monday D0 Online Exercise 4 W Energy tutorial Do HW2 UD Scale Model of Solar System Next week lab for M TuW 3 Moons of Jupiter for Th 2 Observing the Sky or 4 Solar Rotation Galileo Galilei 15641642 First man to point a telescope at the sky wanted to connect physics on earth With the heavens 35 The Nature of Science Our goals for learning HOW can we distinguish science from nonscience What is a theory in science The Scienti c Method 1 Question 2 Hypothesis a tentative explanation 3 Prediction 4 Test 5 Result confirm reject or modify should be the same no matter who conducts the test Hallmarks of Good Science Science seeks explanations for observed phenomena that rely solely on natural causes Science progresses through the creation and testing of models of nature that explain the observations as simply as possible 0 Occam s Razor A scienti c model must make testable predictions that could force us to revise or abandon the model ThQOFy a model which survives repeated testing Bad Scienti c Practice pseudoscience masquerades as science but does not follow the scienti c rules of evidence nonscience establishes truths through belief 36 Astrology Our goals for learning How were astronomy and astrology related in the past and are they still related today Astrology claims to study how the positions of the Sun Moon amp planets among the stars in uence human behavior was the driving force that advanced ancient astronomy Kepler amp Galileo were the last astronomers to cast horoscopes since then astronomy grew apart from astrology into a modern science modern scienti c tests of astrology fail it is a pseudoscience Pop Quiz Do you believe the astrological positions of other planets affect your daily life Carl Sagan s Cosmos The remainder of Class was devoted to Viewing Chapters 812 of Disc III Harmony of the Worlds from Carl Sagan s Cosmos series These excerpts can also be Viewed Via YouTube at httpWwwyoutubecornwatchvxsX6BeBOorA