Astronomy 101The Incredible ExpandingUniverse8/6/09Astronomy 101Astronomy Picture of the DayAstronomy 101Outline for TodayAstronomy Picture of the DayReturn Lab 11Q&A SessionDistance LadderHubble's LawDark EnergyMinute WritingBreakLab 12 – Hubble's LawAstronomy 101Questions for TodayHow are distances found in astronomy?What is the connection between distance andredshift?How is the size of the Universe changing overtime?What is dark energy?Astronomy 101Distance LadderRadar RangingRedshiftSupernova/Tully FisherCepheidsMain Sequence FittingParallaxRadar RangingAstronomy 101Distance LadderParallaxRedshiftSupernova/Tully FisherCepheidsMain Sequence FittingParallaxRadar RangingAstronomy 101Distance LadderMain Sequence FittingRedshiftSupernova/Tully FisherCepheidsMain Sequence FittingParallaxRadar RangingStandard CandlesAstronomy 101Distance LadderCepheidsRedshiftSupernova/Tully FisherCepheidsMain Sequence FittingParallaxRadar RangingStandard CandlesAstronomy 101Distance LadderCepheidsAstronomy 101Distance LadderSupernova/Tully FisherRedshiftSupernova/Tully FisherCepheidsMain Sequence FittingParallaxRadar RangingStandard CandlesAstronomy 101Distance LadderWhite Dwarf SupernovaAstronomy 101Distance LadderTully Fisher RelationshipAstronomy 101Distance LadderRedshiftRedshiftSupernova/Tully FisherCepheidsMain Sequence FittingParallaxRadar RangingAstronomy 101Suppose our estimates of distances of nearbyCepheids found through Main Sequence fittingare uncertain by 30%.Much more distant Cepheids measure in othergalaxies will have distance uncertainties thatA) Increase with distanceB) are at most 30%C) are at least 30%D) depend on the galaxyAstronomy 101Suppose our estimates of distances of nearbyCepheids found through Main Sequence fittingare uncertain by 30%.Much more distant Cepheids measure in othergalaxies will have distance uncertainties thatA) Increase with distanceB) are at most 30%C) are at least 30%D) depend on the galaxy16Almost All Galaxies are Moving AwayFrom Us; Galaxies Far Away From Us AreMoving FasterMeasure theredshift “z” ->derive the“recessionalvelocity”17Hubble’s Original DataDistanceVelocity18A More Recent “Hubble Diagram”Recessionalvelocity isproportional todistance.DHv0=H0 is theslope of thislineH0 is the “HubbleConstant”, unitsare km/s/Mpc19A galaxy’s recessional velocity letsyou estimate its distance.zcv !=Measure…Then use:D = v/H020A galaxy appears to be receding at7500 km/sH0 = 70-75 km/s/MpcDHv0=The galaxy’sdistance is probablyclosest toA) 10 MpcB) 50 MpcC) 100 MpcD) 1000 Mpc21A galaxy appears to be receding at7500 km/sH0 = 70-75 km/s/MpcDHv0=The galaxy’sdistance is probablyclosest toA) 10 MpcB) 50 MpcC) 100 MpcD) 1000 Mpc22Redshifts Give Us Distances ->A 3-D MapAngular distribution of bright galaxies on thesky23The First “Redshift Map”Velocity (distance)Velocity (distance)You are here24Full Circle “Redshift Map”“Fingers of God”What could cause“redshifts” ofgalaxies?What sort ofsituation wouldcause this tohappen?25Full Circle “Redshift Map”“Fingers of God”“Fingers of God”are artifacts.Produced byrandom motion ofgalaxies in clusters26The SloanDigital SkySurvey(SDSS) --has spectrafor 675,000galaxies!27What does the Hubble Law mean?DHv0=Astronomy 101Cosmological Principal The universe looks about the same no matter whereyou are within itMatter is evenly distributed on very large scales in theuniverseNo center & no edgesNot proved but consistent with all observations to date (i.e. You are not special)29The Hubble Law implies that theentire UniverseUniverse is expanding!Occurs in every direction!DHv0=Astronomy 101DistanceVelocity Away From UsAstronomy 101The “Cosmological Redshift”Photons that travel for longer (from further away),have experienced more expansion.Bigger Distance = Bigger RedshiftFurther seems Faster!Astronomy 101But if the Universe is expanding,won’t the Solar System eventuallyexpand apart?A) The Solar System may actually be shrinkingnow, which makes the Universe LOOK like it’sexpandingB) No, its gravity holds it togetherC) No, because there is no planetary redshiftD) Eventually, but only after a very long timeAstronomy 101But if the Universe is expanding,won’t the Solar System eventuallyexpand apart?It’s not hard for other forces to be strongerthan the push of expansion.None of these areexpanding!They are bound together byelectricity and/or gravity!Astronomy 101Distancesbetweenfarawaygalaxieschange whilelight travelsAstronomersthink in termsof lookbacktimedistance?How does the expansion of theUniverse effect our understanding ofdistance?Astronomy 101Not An “Explosion”No CenterNo EdgeNot Expanding Into AnythingAstronomy 101Not An “Explosion”No CenterNo EdgeNot Expanding Into AnythingThere was a beginning . . .Astronomy 101Your friend leaves your house. She latercalls you on her cell phone, saying thatshe’s been driving at 60 miles an hourdirectly away from you the whole timeand is now 60 miles away. How long hasshe been gone?A. 1 minuteB. 30 minutesC. 60 minutesD. 120 minutesAstronomy 101Your friend leaves your house. She latercalls you on her cell phone, saying thatshe’s been driving at 60 miles an hourdirectly away from you the whole timeand is now 60 miles away. How long hasshe been gone?A. 1 minuteB. 30 minutesC. 60 minutesD. 120 minutesAstronomy 101Your friend leaves your house. She latercalls you on her cell phone, saying thatshe’s been driving at 60 miles an hourdirectly away from you the whole time andis now 60 miles away.TimeDistance from Your HomeAstronomy 101TimeDistance from Your HomeYour friend leaves your house. She latercalls you on her cell phone, saying thatshe’s now driving at 60 miles an hour andwas driving more slowly directly awayfrom you the and is now 60 miles away.Astronomy 101TimeDistance from Your HomeYour friend leaves your house. She latercalls you on her cell phone, saying thatshe’s now driving at 60 miles an hour andwas driving faster directly away from youthe and is now 60 miles away.Astronomy 101You see a galaxy some distance away thatis retreating from you. When was thedistance between it and you zero?TimeDistance to the galaxyH0 = 70-75 km/s/MpcAstronomy 101You see a galaxy some distance away thatis retreating from you. When was thedistance between it and you zero?TimeDistance to the galaxyH0 = 70-75 km/s/MpcInverse of Hubble’s Constant ~ Age of the Universe1/H0 ~ 14 Billion YearsAstronomy 101You see a galaxy some
View Full Document
Unlocking...