The truth about star colors

[skysurfer]

In many publications the spectral classes are colored as follows:

O - blue
B - bluish white
A - white
F - yellowish white
G - yellow
K - orange
M - red

With my experience in many cases this is NOT true. Look at Canopus it is white with a bluish tinge, particularly when looking with a telescope or binoculars and then is it visible with many other brighter F stars like Procyon or Polaris.
Same with the 'yellow' G-stars Capella or Alpha Centauri, they look ... white.
So called 'red' stars which are bright (Antares, Betelgeuse) look like a remote halogen bulb or warmwhite LED lamp, which has the same (color) temperature.
Only in daylight, Alpha Centauri and Capella look yellowish in the telescope but that is the contrast to the blue sky.
A 5800K color temp CFL or metal halide lamp (same color temp as G stars) looks white.

What are your ideas ?

[mithrandir (Andrew)]

See http://outreach.atnf.csiro.au/educat...ry_colour.html

The section headed "Human Vision" gives an outline of why what you see is not how the colour is described.

Also see http://adsabs.harvard.edu/full/1946BAN....10...99W for a discussion of black body radiation with formulae.

[skysurfer]

Interesting article.

But the picture of Orion in this article shows the defocused Betelgeuse indeed the same yellowish color as a halogen lamp.

[Robh (Rob)]

The alpha Centauri pair do look yellowish to me. Sometimes colour can look different in binoculars, different types of scopes (refractor or Dob) or using different EPs.
Canopus does look white. Its spectral type is F0. I would expect it to look white (more on that below).
Apart from the limitations of colour perception at night, you need to expand your ideas on spectral class.

Each spectral class is subdivided from 0 to 9 (e.g. G0, G1 ... G9) and sometimes divided further again e.g. M1.5. Change in colour is on a continuum. Yellow does not change into orange at a discrete point. The centre of each class is more representative of the colour assigned to that class. Thus, a G8 or G9 spectral type star is not so different from a K0 or K1 type star. They will all appear yellow. Antares (M1.5) and Betelgeuse (M1-M2) are not that much different from a K8, K9 type star i.e. they appear orange.

Regards, Rob

[Jon (Jonathan)]

Originally Posted by skysurfer

Interesting article.

But the picture of Orion in this article shows the defocused Betelgeuse indeed the same yellowish color as a halogen lamp.

I think that's more to do with how the colour in the article appears on computer screens - another whole dimension to colour perception that we have to deal with nowadays. Defocused Betelgeuse is definitely orange-red in my scope - although as a bright point-source can still seem whitish.