Blue Flame hotter then yellow-orange, but what about purple or indigo?

Question

So I hear the the more towards the blue spectrum a flame or star goes the hotter it becomes. We cant see ultra violet (UV) colors but we can see violet. So would a pupleish flame or star be hotter then blue?

Answer 1

The blue color of a flame arises from different mechanisms than the yellow color does.  The yellow color comes from incandescent carbon particles in the flame that result from incomplete combustion of the fuel.  Blue flames get their color instead from emissions of free radicals in the flame - this is not the same as a very hot star emitting blue light.  The blue flame is hotter, but I think this is just because the fuel is being burned completely.

The incandescent particles emit nearly as black body radiators - they emit a distribution of wavelengths with a peak that moves towards the UV as the sample is heated.  My guess would be that due to this distribution and due to how human vision works, we never see violet flames as the other emissions would combine to form a more bluish/whitish light when the peak emission is in the violet.  See the link for more info on how these particles emit light.

Answer 2

Think in terms of the visible light spectrum here.  We've got:

Red

Orange

Yellow

Green

Blue

Indigo

Violet

I've listed them in order from longest wavelength to shortest wavelength.  Also, that order represents lowest frequency to highest frequency.

When light is emitted from a radiating body, the color of the light reflects the amount of energy that body has.  So the hotter a star is, the more energy it will have.  Therefore, if violet light shines from a star, that star has more energy than a star with blue light and consequently has a higher temperature, because stars are not much more than burning balls of gas and mineral.