Doppler shifted hydrogen absorption lines are seen in the spectrum of a star. The hydrogen line at 656.28 nm is seen to be shifted to 656.08 nm. The star is moving at which fraction of the speed of light?

Question

Quizplus · Accepted Answer

The Doppler shift formula for light is Δλ/λ = v/c, where Δλ is the change in wavelength, λ is the original wavelength, v is the velocity of the star, and c is the speed of light. Here, Δλ = 656.08 nm - 656.28 nm = -0.20 nm, and λ = 656.28 nm. Solving for v/c gives approximately 0.0003.

Doppler Shifted Hydrogen Absorption Lines Are Seen in the Spectrum