The observed change in wavelength of light due to the Doppler effect occurs:
A) only when the temperature of an object changes.
B) only when the light source has proper motion (i.e., motion across the line of sight).
C) whenever the light source is moving with respect to the observer (regardless of direction).
D) only when the light source has a radial velocity (i.e., motion toward or away from the observer).

Question

Quizplus · Accepted Answer

The Doppler effect causes a change in the wavelength of light only when the light source has a radial velocity, i.e., motion toward or away from the observer. This effect is observed in many astronomical objects, such as stars, galaxies, and quasars, allowing astronomers to measure their velocities along the line of sight. The temperature of an object or the proper motion of the light source does not affect the Doppler shift.

The Observed Change in Wavelength of Light Due to the Doppler