Absorption lines due to interstellar gas
A) are wider than the lines from stars because the gas is hotter than most stars.
B) are more narrow than the lines from stars because the gas has a lower pressure than stars.
C) indicate that the interstellar medium contains dust.
D) indicate that the interstellar medium is expanding away from the sun.
E) none of the above.

Question

Quizplus · Accepted Answer

Absorption lines due to interstellar gas are more narrow than the lines from stars because the gas has a lower pressure than stars. The gas in interstellar space is much less dense than the gas in stars, and so the collisions between atoms or molecules that would widen the spectral lines are less likely to occur.

Absorption Lines Due to Interstellar Gas