Why are Balmer absorption lines very weak in the spectra of stars with low surface temperatures-significantly below 10,000 K, for example?
A) The hydrogen atoms have to be hot enough to be ionized in order to show Balmer absorption.
B) There is no emitted continuum radiation at Balmer-line wavelengths when the gas is so cool, so absorption will not be seen.
C) Atoms need electrons that have been excited by high temperatures to the n = 2 level to undergo Balmer absorption.
D) Hydrogen atoms have no electrons in any energy levels at these temperatures.

Question

Quizplus · Accepted Answer

At low surface temperatures, most hydrogen atoms are in the ground state (n = 1) and not enough are excited to the n = 2 level, which is necessary for Balmer absorption to occur.

Why Are Balmer Absorption Lines Very Weak in the Spectra