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Hubble’s Law: Measuring the Age of the Universe Dr Lisa Jardine-Wright Cavendish Laboratory, University of Cambridge
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General Theory of Relativity: –Told astronomers that the Universe was either expanding or contracting depending on the amount of Mass and Energy in the Universe –Einstein didn’t like this idea so modified his theory to ensure that the Universe was static. Einstein 1915
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1926 - 29 Hubble’s Observations
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Using cutting edge data and images we are going to reproduce Edwin Hubble’s observations. To do this we need to measure the distance and velocity to a number of spiral galaxies and see if we observe a relation between these two quantities. Experiment
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Part 1: Distance
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Galaxy Size (mm) Distance (Mpc) CaKCaHAverage z Velocity (km/s) λ Z 1 =(λ - 3933.7) 3933.7 λ Z 2 =(λ - 3968.5) 3968.5 Z = z 1 +z 2 2 v=cz (c = 3x10 5 km/s) NGC 1357 NGC 2276 NGC 2903 NGC 3627 NGC 4775 NGC 6181 NGC 6643 NGC 1832 NGC 5248
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Part 1: Distance
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Galaxy Size (mm) Distance (Mpc) CaKCaHAverage z Velocity (km/s) λ Z 1 =(λ - 3933.7) 3933.7 λ Z 2 =(λ - 3968.5) 3968.5 Z = z 1 +z 2 2 v=cz (c = 3x10 5 km/s) NGC 1357 NGC 2276 NGC 2903 NGC 3627 NGC 4775 NGC 6181 NGC 6643 NGC 1832 NGC 5248
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Part 2: Velocities White light can be split into its component colours or wavelengths –Spectrum
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Part 2: Velocities How do we measure the velocities of distant galaxies? –Redshift - The astronomical Doppler effect
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Part 2: Velocities Different chemicals absorb and emit light of different colours or wavelengths.
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Part 2: Velocities The wavelength of the emission and absorption lines from elements in our galaxy are redshifted due to their velocity away from us. –If we can measure how much they are shifted we can calculate their velocity λ 0 = wavelength of line in the Lab, v = velocity of the galaxy and c = speed of light
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Example λ = 3962, λ 0 = 3933.7, c = 3 x 10 5 km/s
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Part 2: Velocities Galaxy Size (mm) Distance (Mpc) CaKCaH Average z Velocity (km/s) λ Z 1 =(λ - 3933.7) 3933.7 λ Z 2 =(λ - 3968.5) 3968.5 Z = z 1 +z 2 2 v=cz (c = 3x10 5 km/s) Example39620.00740000.0080.00752250 NGC 2276 NGC 2903 NGC 3627 NGC 4775 NGC 6181 NGC 6643 NGC 1832 NGC 5248
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Hubble’s Law Galaxy Size (mm) Distance (Mpc) CaKCaH Average z Velocity (km/s) λ Z 1 =(λ - 3933.7) 3933.7 λ Z 2 =(λ - 3968.5) 3968.5 Z = z 1 +z 2 2 v=cz (c = 3x10 5 km/s) NGC 1316 NGC 2276 NGC 2903 NGC 3627 NGC 4775 NGC 6181 NGC 6643 NGC 1832 NGC 5248
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Hubble’s Law
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