Stellar Spectral Classes
F Yellow White
O 30 to 60 thousand degrees Kelvin
B 10 to 30
A 7,500 to 10,000 degrees kelvin
F 6,000 to 7,500
G 5,000 to 6,000
K 3,500 to 5,000
M 2,000 to 3,500
The seven classes are each subdivided into tenths from 0 to 9. Sol is G2. Korych, the sun of Merseia, is Sol-like. Cerulia, the sun of Vixen is F-type. The eye structure of the Ardazirho invaders of Vixen suggests that their sun is about A5, which would be no good for human beings. F is probably as cool as Ardazirho would want.
Flandry thinks that the Ardazirho "'...may well have built up a little coterminous kingdom, a number of B, A and F suns...'" (Sir Dominic Flandry, p. 201), before invading Vixen.
The Dispersal of Ymir interpenetrates the Terran Empire and the Merseian Roidhunate because the Ymirites occupy not terrestroid planets but gas giants, including Jupiter in the Solar System and Ogre in the Cerulian System. Thus, the Dispersal probably continues to exist after the Fall of the Empire and the collapse of the Roidhunate but might there also be other coterminous realms in the systems of stars with different spectral types?