Stellar classification

Stellar classification was used to assign classes to stars based on certain characteristics.

Human classification
The Tenth Doctor knew of and used the human-designed Harvard spectral classification. Accidentally arriving on the planet Sunday, the Doctor wondered why Arkon (his intended destination) had an orange star, instead of a hot, white class F star. This led him to believe that either the Arkonides had experimented with stellar manipulation, or that he was on the wrong planet. (PROSE: Wetworld)

Behind the scenes

 * PROSE: Wetworld uses a classification system that includes classes from the Harvard System; however, at no point is it directly referred to as such.