An astronomer photographs the spectrum of an object 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:
A)away from Earth at 499/500 the speed of light.
B)away from Earth at 1/500 the speed of light.
C)toward Earth at 499/500 the speed of light.
D)toward Earth at 1/500 the speed of light.

Question

Quizplus · Accepted Answer

The object is moving toward Earth because the observed wavelength (499 nm) is shorter than the laboratory wavelength (500 nm), indicating a blue shift. The speed can be approximated by the difference in wavelength divided by the rest wavelength, which gives 1/500 the speed of light.

An Astronomer Photographs the Spectrum of an Object and Finds