Two stars on the main sequence of an H-R diagram are equally bright in BLUE light, with one brighter in RED?

Question

Which one is hotter, and which one is further away? AND why?

Answer 1

Since the (say, "A" and "B") stars have the same luminosity in blue, the star with the greater red luminosity (say star "B") is the cooler. "B" is producing energy of longer wave lengths that "A", and since there is more of that light, the star has to be cooler to produce it. On the other hand, the total luminosity of "B" is greater, since it is bright across the spectrum, so it must be the further away.

HTH

Charles