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At what wavelength would its Lyα line be received by a detector above Earth's atmosphere?

Express your answer using four significant figures.

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A distant galaxy is receding from Earth with a radial velocity of 7000 km/s .
The Lyα line has a wavelength of 121.6 nm. Using the Doppler Effect formula:
λ_obs = (121.6 nm) x (1 + (7000 km/s) / (300000 km/s)) = 124.4 nm
User Stephen Kuo
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