Transcript: Since hydrogen is the most abundant element in the universe and in stars, its spectral transitions are fundamental to stellar classification. The ground state is numbered n = 1, an electron in the lowest energy level it can have. States then go up, n = 2, n = 3, increasing in number at higher excitations from the ground state and closer and closer spacings until the atom is ionized. Transitions in and out of the n = 1 state appear mostly in the ultraviolet part of the spectrum and are called the Lyman series. Transitions in and out of the n = 2 state appear in the visible part of the spectrum and are called the Balmer series. Among the Balmer series the most prominent line is H-alpha or hydrogen-alpha involving transition between n = 2 and n = 3 states.