A spectral line produced in the atmosphere of a star may be seen as broad whereas interstellar _______________ lines are very narrow.
A)absorption
B)continuous
C)emission
D)All of the other choices are correct.

Question

Quizplus · Accepted Answer

Absorption lines are produced when light from a star passes through the cooler layers of gas in its atmosphere, and some of the light is absorbed by the atoms and molecules in the gas. This results in dark lines in the spectrum of the star, and the width of these lines depends on the temperature and pressure of the gas. Interstellar absorption lines, on the other hand, are produced by the absorption of light from a background source by gas clouds in the interstellar medium. These lines are very narrow because the gas in the interstellar medium is much colder and less dense than the gas in stellar atmospheres. Continuous and emission lines are not relevant to this comparison.

A Spectral Line Produced in the Atmosphere of a Star