How can hydrogen spectral lines identify hydrogen in stars?

Hydrogen is identified in stars through the analysis of its spectral lines, which are characteristic of the element. When atoms are excited, they radiate or absorb light at specific, discrete wavelengths determined by transitions between quantum states.12

In stellar atmospheres, hydrogen typically produces absorption lines as atoms absorb photons at these specific wavelengths. The intensity and shape of these lines provide critical information:23

• Identification: Because the wavelengths of these lines are unique to hydrogen, their presence in a star's spectrum confirms the element's existence. The Balmer series, located in the visible region, is particularly well-known for this purpose.12
• Physical Conditions: The appearance of these lines is influenced by the star's temperature and atmospheric density. For example, hydrogen lines reach maximum intensity in A-type stars (about 9,000 K) and fade in hotter stars as hydrogen becomes ionized. Additionally, the width of these lines can indicate the star's surface gravity, with broader lines often appearing in denser dwarf stars.34