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Originally Posted by George
Why is this? Shouldn't the color label represent the color?
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Actually its based more on stellar surface temperature -this affects colour eg. hotter = bluer, cooler = redder but there a real whole lot of complicating factors such as dust which reddens them, the sensitivity of the human eye and the subtlety of star colours generally.
There could easily be
(& perhaps already is) a whole other thread on this "colour of the stars" topic.
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No apologies necessary. I undestand where you're coming from and it is likely me that is belabouring the issue. I do it partly to have some fun with it because I honestly think it is something somewhat trivial, yet I think it doesn't hurt to recognize true color, when available, just for the sake of knowledge, if nothing else. Even though color is often subjective, I suspect that this is not the case for the Sun; there is enough objective evidence for an air-tight case against the Sun being yellow.
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Thanks. Star types - their spectral & luminosity classes - are one of my favourite areas & I'm always happy to discuss 'em.
I'm pretty sure the colour of our Sun was discussed by the BA in his first book -
'Bad Astronomy' I think twas called - but, unfortunately, I can't seem to find my copy anywhere -think I've lent it out & have not had it returned. :-(
From what I recall, the Sun is usually described & commonly perceived as yellow esp. in artwork but is in fact white & would appear white if we went above earth's atmosphere - although it actually puts out most of its energy at the "green" wavelength.
[quote] I had thought that most white dwarfs were hotter and I have not seen a white dwarf cool enough to be red, but, of course, once they do cool down, they should become red in color. Are there some red ones known? I hope so. [quote]
In his
'100 Greatest Stars' (Copernicus Books, 2002) book Kaler includes the fiantest white dwarf ESO 439-26 noting on page 75 :
"We might expect the faintest white dwarfs to be coolest, but while ESO 439-26's luminosity may be lowest, its temperature is not. At 4560 K, it is warmer than the current record of 3500 for a somewhat brighter star called WD 0346+246. (At these temperatures, white dwarfs are reddish showing the danger in naming clases of objects before they are understood.)"
(Brackets original.)
I think Van Maanen's Star - the third nearest after Sirius B and Procyon B and nearest single white dwarf in our skies is also extremely cool, small and ancient.
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That seems like a nice way to handle that and I had not seen this before. Thanks. This is somewhat important since how will we change the yellow dwarf Sun to a white dwarf Sun and avoid confussion. [I honestly don't think we will always in the future call the non-yellow Sun a yellow dwarf, but I could be wrong.]
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Afraid I'd have to disagree on that last line there - I think the term is too well established to be changed and, as noted, its based on the surface temperature idea more than the colour one anyhow. I suppose I can see the possibility of 'main-sequence' or 'normal' star taking over from "dwarf star" with the latter then applying to white dwarfs & maybe brown dwarfs only, but I'm not sure that even the chances of that are high. Just my gut feeling there. Once terms are established it is very hard to change them as there's a large amount of pyschological terminological inertia to overcome.
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I appreciate such a thorough post. Though it's not a big deal, the Sun, however, remains not a yellow star.
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My pleasure! :-)
Great link there too complete with true colour picture of Sun & planets & 18 Scorpii image too.
"Who knows what color lurks hidden behind the blaze of Sun? The heliochromologist knows!" could make a great signature line! ;-)
Yeah, I'd have to agree in the sense that our wouldn't appear yellow or at least very yellow-ish although in the classification sense it is! ;-)