The Niels Bohr model of the atom gave a very accurate explanation of the hydrogen spectrum, but when it came to helium, it collapsed.

In contrast, there are also helium-weak B-type stars with understrength helium lines and strong hydrogen spectra.

It then looks at the antihydrogen spectrum in order to compare it against "normal" hydrogen spectrum.

When lines of the hydrogen spectrum are examined at very high resolution, they are found to be closely spaced doublets.

The star has blurred lines in its hydrogen spectrum due to its rotation.

It accounted for the fine details of the hydrogen spectrum in a completely rigorous way.

Historically, explaining the nature of the hydrogen spectrum was a considerable problem in physics.

Nobody could predict the wavelengths of the hydrogen lines until 1885 when the Balmer formula gave an empirical formula for the visible hydrogen spectrum.

Later, it was discovered that when the spectral lines of the hydrogen spectrum are examined at very high resolution, they are found to be closely spaced doublets.

Balmer noticed that a single number had a relation to every line in the hydrogen spectrum that was in the visible light region.