spectroscopy - Why are there multiple lines in the hydrogen line spectrum?

Hydrogen has only one electron, yet it exhibits multiple lines in a spectral series, why is this?

Answer

As the electrons fall from higher levels to lower levels, they release photons. Different "falls" create different colors of light. A larger transition releases higher energy (short wavelength) light, while smaller transitions release lower energies (longer wavelength).

The visible wavelengths are caused a by single electron making the different transitions shown below. There are even more transitions that release invisible wavelengths.

 Wavelength   Transition  Color              
 (nm)                                        
---------------------------------------------
 383.5384      9 -> 2    Ultra Violet
 388.9049      8 -> 2    Ultra Violet
 397.0072      7 -> 2    Ultra Violet
 410.174       6 -> 2    Violet
 434.047       5 -> 2    Violet
 486.133       4 -> 2    Bluegreen (cyan)

 656.272       3 -> 2    Red
 656.2852      3 -> 2    Red

*Values taken from Hyperphysics: Hydrogen Energies and Spectrum

(Why are there two different 3-> 2 transitions? See here: Hydrogen Fine Structure )