Lab 10 - Physics & Astronomy

Astronomy 105 LaboratoryLAB 10

Lab 10HUBBLE’S LAW

Edwin Hubble(1889-1953)• Measured distances to nearbygalaxies using Cepheid variables• Galaxies are islands of stars• Developed a classificationscheme for galaxies.• Discovered the Expansion of theUniverse• Space telescope named after him!

Hubble’s Law• Hubble Measured distances tonearby galaxies using Cepheidvariables• Other astronomers measuredgalaxy velocities (redshifts)Hubble DiagramRedshifts

Recessional Velocity is Proportional to Distance10 Mpc 20 Mpc 30 Mpc 40 MpcMilkyWay A B C1400700V = 0 70014002100 2800km/sec40 Mpc30 Mpc20 Mpc 10 Mpc Alien’sGalaxyMilkyWay A B C10 Mpc 20 Mpc2800 2100 1400700V = 07001400km/secThe Universe is Expanding!!

Hubble’s LawHubble Diagramy = mx + bEquation of aStraight Liney - recessional velocity(v) x - distance(d)m = slope = Hubble’s Constant (H o )Hubble’s Lawv = H o d

Finding a Galaxy’s DistanceHubble’s LawHubble Diagramv = H o dd = v / H oTo Find Distance: Measure recessional velocity (red shift)132 Mpc

Estimating the Age of the Universe60 mph, 120 mi 60 mph, 120 mitime distancevelocity240 miles120 miles/hour 2hoursM100t = 0Milky WayHubble’s Lawv = H o dt = presenttdvdH d1oH o

Example: H o = 60 km/s/Mpct1Ho160 km/s/Mpc1 s Mpc60 kmconversion193.110km1Mpct1Ho160s Mpckm 19 3.16 10km 1 Mpc5.3 1017sconversion1yr3.16 107st1Ho17 1 yr 105.310s 1.7 10yr 3.16 107s t = 17 billion years

Important: Do not write or mark on theHubble Handout

d 15.6 Mpc 49.4 mmS Sample Galaxies• Distance images• Recessional Velocity spectra

Measuring Distance• Elliptical galaxies - same physical size (0.032 Mpc)• Virgo – known distance of 15.6 Mpc• Distances inversely proportional to angular sized = 15.6 Mpc49.4 mmSMeasure to nearest 0.5 mm1.0 mm

Measuring Recessional VelocityH line388.8 nm 112.7 nm501.5 nmL – measure distance (mm) between the 388.8 nm and the 501.5 nm emission linesx – measure distance (mm) between the 388.8 nm line and the H lineλ o = 396.8 nm (laboratory wavelength of the H line)Observed Wavelength of H Lineλ obs = 388.8 nm +xL(112.7 nm)Recessional Velocityv =c (λ obs – λ o )λ o

Hubble DiagramHubble Diagramv = H o x dxxxriseProcedure- plot data- draw best fit line- find slope (H o )xxrunslope = rise/run

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