H-alpha

In physics and astronomy, H-alpha, also written Hα, is a specific emission line created by hydrogen. According to the Bohr model of the atom, electrons exist in quantized energy levels surrounding the atom's nucleus. These energy levels are described by the principal quantum number n = 1, 2, 3, ... . Electrons may only exist in these states, and may only transition between these states. The set of transitions from n ≥ 3 to n = 2 are called the Balmer series and are named sequentially by Greek letters: n = 3 to n = 2 is called Balmer-alpha or H-alpha, n = 4 to n = 2 is called H-beta, n = 5 to n = 2 is called H-gamma, etc.
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