Question:
The 6563 Å Hα line emitted by hydrogen in a star is found to be red-shifted by 15 Å. Estimate the speed with which the star is receding from the Earth.
Solution:
λ = 6563 Å
Δλ = 15 Å
Since the star is receding, the velocity (v) is negative.
Δλ = – vλ/c
v = – cΔλ/λ
= – (3 x 108) x (15 Å/ 6563 Å)
= – 6.86 x 105 m/s
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