ASTRONOMY 2010

# ASTRONOMY 2010 - What is fractional shift in...

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ASTRONOMY 2010: 01-15-08 Hubble’s Law: v = H 0 D (velocity km/sec; Distance M pc) v~D 01-17-08 Hubble’s data gave: H 0 = 500 km/s/Mpc v = H 0 D Measure the v Hubble Constant Measure galaxy distance from the Doppler in (km/s per Mpc) by independent means shift (redshift) Recent Measurements of the hubble Expansion Rate: H 0 =72±10% v=H 0 D D = v / H 0 (measure velocity and use calibrated value of H 0 ) Note: The smaller H 0 , the larger the distance (and the older the universe) Estimate of Age of Universe: Earth Galaxy D v How long has galaxy been traveling? D = v t where v = H 0 D So that t = D/v = D/(H 0 D) = 1/H 0 H 0 = 75 km/s/Mpc t 0 = 13 Gyr Light and Sound are Waves: Wavelength (λ) gives the color of light; visible Light ranges from 4000 to 7000 Angstoms 1 Angstrom = 10 -10 m 1 nm = 10 -9 m (7000 A = dark red; 4000 A = violet) Wavelengths stretch or compress Doppler Effect: Police Siren:

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Unformatted text preview: What is fractional shift in wavelenghts? [also in pitch or frequency] v = 70mph c s = 700mph Velocity of Doppler Shift: v / c = Δλ / λ = z v= c z (z is called the “Redshift”) Example: 5% shift in wavelenght means that v = 0.05c Example (Dopller Efect): Using Light (EM waves) Rest Wavelength λ = 5000 A Observed at λ = 5050 A What is the Redshift? Wavelength Shift Δλ = 50 A z = Δλ/λ = 50/5000 (1% shift or z = 0.01) The Δλ = 50 A wavelength shift corresponds to a redshift z = 0.01 Doppler formula v ≈ c z = 0.01 The speed of light is c ≈ 300,000 km/s Galaxy is moving at 0.01 c (v = 3000 km/s) D = v/H = (3000 km/s) / (75 km/s/Mpc) ≈ 40 Mpc (or 130 million lt-yrs) Milky Way Galaxy: R = 8.2 ± 0.3...
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## This note was uploaded on 04/02/2008 for the course ASTR 2010 taught by Professor Shull during the Spring '08 term at Colorado.

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ASTRONOMY 2010 - What is fractional shift in...

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