A gas cloud has an emission spectrum.If all of its lines appear at higher photon energies than expected from a comparison to laboratory measurements,the cloud is:
A) cooler than the laboratory gas.
B) hotter than the laboratory gas.
C) moving away from the observer.
D) moving toward the observer.

Question

Quizplus · Accepted Answer

When the emission lines of a gas cloud appear at higher photon energies (or shorter wavelengths) than expected, it indicates a blueshift, which occurs when the gas cloud is moving toward the observer.

A Gas Cloud Has an Emission Spectrum