The spectrum of a star shows a set of dark absorption lines equivalent to the absorption lines of the Sun but with one exception: Every line appears at a slightly longer wavelength, shifted toward the red end of the spectrum. What conclusion can be drawn from this observation?
A) A cloud of cold gas and dust surrounds the star and is absorbing light from it.
B) The star is moving toward Earth.
C) The temperature of the star's surface is higher than that of the Sun.
D) The star is moving away from Earth.

Question

Quizplus · Accepted Answer

This observation is a classic example of the Doppler effect, where the wavelength of light from an object increases (redshift) if the object is moving away from the observer.

The Spectrum of a Star Shows a Set of Dark