Astronomers can tell whether a star is approaching or receding from earth by
A) the Doppler effect.
B) its temperature.
C) its change in temperature.
D) its absorption spectra.
E) all of these

Question

Quizplus · Accepted Answer

The Doppler effect explains how the frequency of light (or sound) waves changes due to the relative motion of the source and the observer. When a star is moving towards us, its light waves are compressed, making them appear bluer (blue shift), and when it's moving away, the waves are stretched, making them appear redder (red shift). This allows astronomers to determine whether a star is approaching or receding from Earth.

Astronomers Can Tell Whether a Star Is Approaching or Receding