Stellar classification

Stellar Classification was used to assign classes to stars based on certain characteristics. At least one type of classification was used in the Doctor Who Universe.

Human Classification
The Doctor knew of and used the Human designed 'Harvard Spectral Classification' method. 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. (NSA: Wetworld)

Classes in the Harvard System
''Classes in this system are assigned on the colour of the star. Some examples are given here.''

O - Blue B - Blue/White A - White F - White/Yellow (Arkon's Star) G - Yellow - (Sol) K - Orange (Sunday's Star) M - Red