hubble’s law. edwin hubble (1889-1953) measured distances to nearby galaxies using cepheid...
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Hubble’s Law
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Edwin Hubble(1889-1953)
• Measured distances to nearby galaxies using Cepheid variables
• Galaxies are islands of stars• Developed a classification scheme
for galaxies.• Discovered the Expansion of the
Universe• Space telescope named after him!
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We measure galaxy distances using a chain of techniques!
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Hubble’s Law
v = Ho x d
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V = 0 2800210014007007001400
km/sec
10 Mpc 20 Mpc 30 Mpc 40 MpcMilky Way A B C
V = 02800 2100 14007007001400
km/sec
10 Mpc 20 Mpc30 Mpc40 Mpc
Milky Way A B C
10 Mpc20 Mpc Alien’s Galaxy
Recessional Velocity is Proportional to Distance
The Universe is Expanding!!
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y = mx + b
m = slope = Hubble’s Constant (Ho)
y - recessional velocity(v) x - distance(d)
Equation of a Straight Line
v = Ho x d
Hubble’s Law
Hubble DiagramHubble Diagram
Hubble’s LawHubble’s Law
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v = Ho x dHubble DiagramHubble Diagram
Finding a Galaxy’s Finding a Galaxy’s Distance Distance Hubble’s LawHubble’s Law
d = v / Ho
To Find Distance: Measure recessional velocity (red shift)
132 Mpc
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Sample Galaxies
• Distance– images
• Recessional Velocity– spectra
S
mm 49.4Mpc 15.6d
S
mm 49.4Mpc 15.6d
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Measuring Distance
• Elliptical galaxies - same physical size (0.032 Mpc)• Distances inversely proportional to angular size• Virgo – known distance of 15.6 Mpc
d = 15.6 Mpc49.4 mm
S
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Measuring Recessional Velocity
388.8 nm 501.5 nm
H line
112.7 nm
L – measure distance (mm) between the 388.8 nm and the 501.5 nm emission lines
x – measure distance (mm) between the 388.8 nm line and the H line
λo = 396.8 nm (laboratory wavelength of the H line)
λobs = 388.8 nm + (112.7 nm)x
L
c (λobs – λo)
λo
v =
Observed Wavelength of H LineRecessional Velocity
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v = Ho x dHubble DiagramHubble Diagram
Hubble DiagramHubble Diagram
Procedure- plot data
- draw best fit line
- find slope (Ho)x
x
x
x
x
rise
runslope = rise/run
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End