Why is it that astronomers rely upon the 21-centimeter line associated with the spin flip in hydrogen and not the more familiar hydrogen Balmer lines to gather information from the far side of the galactic plane?
A) The Balmer lines are associated with neutral hydrogen, and most of the hydrogen astronomers need to observe is molecular hydrogen.
B) The Balmer lines are associated with molecular hydrogen, and most of the hydrogen astronomers need to observe is neutral hydrogen.
C) The Balmer lines are in the visible and ultraviolet regions of the spectrum, and these do not penetrate the gas and dust clouds easily.
D) Photons released in the spin-flip transition have much more energy than those that come from the Balmer transitions.

Question

Quizplus · Accepted Answer

The 21-centimeter line, being in the radio part of the electromagnetic spectrum, can penetrate gas and dust clouds more easily than the Balmer lines, which are in the visible and ultraviolet regions and are more readily absorbed or scattered by the interstellar medium.

Why Is It That Astronomers Rely Upon the 21-Centimeter Line