An astronomer measures the spectrum of a star and finds a spectral line at 499 nm wavelength. In the laboratory, this spectral line occurs at 500 nm. According to the Doppler effect, this object is moving _____ Earth at _____the speed of light.
A) toward; 1/500
B) away from; 1/500
C) toward; 499/500
D) away from; 499/500

Question

Quizplus · Accepted Answer

The star's spectral line is blue-shifted (shifted to a shorter wavelength) from 500 nm to 499 nm, indicating it is moving toward Earth. The speed can be approximated by the change in wavelength divided by the original wavelength, which is (500 - 499)/500 = 1/500 of the speed of light.

An Astronomer Measures the Spectrum of a Star and Finds