ASsume we measure the 21-cm line of atomic hydrogen from a gas cloud in the Milky Way. We measure the wavelength of hydrogen line to be 21.11223 cm. The rest wavelength is 21.10611 cm. What is the radial velocity of the gas cloud? Is it moving toward or away from us?
Completely lost, any help would be appreciated!
Completely lost, any help would be appreciated!
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The Hydrogen line observed in the gas cloud has been redshifted compared to the same Hydrogen line we observe in the lab. The gas cloud is therefore moving away from us.
If v << c, then, by the Doppler effect;
λ1 / λ0 = 1 + v/c
(λ1 / λ0 - 1)c = v
(21.11223 / 21.10611 - 1) * 299792458 = v
2.900 x 10^(-4) * 299792458 = v
v = 86,929 m/s
If v << c, then, by the Doppler effect;
λ1 / λ0 = 1 + v/c
(λ1 / λ0 - 1)c = v
(21.11223 / 21.10611 - 1) * 299792458 = v
2.900 x 10^(-4) * 299792458 = v
v = 86,929 m/s