by Ann » Wed Jun 30, 2010 8:09 am
Chris Peterson wrote:Ann wrote:Chris, since you are the staunch defender of the idea that the Sun is yellow...
Why do you say that? I consider the Sun to be white
Wow! Thanks, Chris! I'll hold you to it.
G stars are called "yellow", a terminology that has nothing to do with their actual apparent color.
![Evil or Very Mad :evil:](./images/smilies/icon_evil.gif)
That's the worst kind of astrospeak. The Sun is defined as a G2 star and therefore it is defined as yellow, which does not, however, God forbid, means that it
is yellow!
I'll keep insisting that the whole sorry bit of color definition in astronomy has everything to do with the fact that Vega has, extremely wrongly, been defined as the ultimate example of stellar whiteness. If Vega is white, then all stars yellower than Vega must be either yellow-white, yellow, orange or red. What a pity: when astronomers finally found the "brown" dwarfs, tiny embers of failed stars which emit only a bit of red light and no other visible light, the term "red dwarf" - which should of course have been given to those puny little red-only stellar midgets - had long ago been given to faint yellow-orange stars like Proxima Centauri. (And to add confusion to confusion: Vega is a "dwarf", because it is very much on the main sequence, and it is defined as "white", because it is the ultimate astronomical definiton of stellar whiteness, so it must be a "white dwarf"... except it is anything but a white dwarf, even though it is [astronomical definition]white[/astronomical definition] and it is a [astronomical definition]dwarf[/astronomical definition]. I hate these super-stupid definitions which seem designed to give you the wrong idea about stars!!!)
Back to the Sun. Chris said this about its light output:
The most intense individual peaks are around 450nm, which looks blue. The blackbody associated with the Sun's temperature, 5800K, has a peak of 500nm, close to cyan. The best fit blackbody to the actual spectrum is 5250K, which has a spectral peak of 555nm, which is the yellow side of green.
Does anyone have any actual "color samples" corresponding to 450nm, 500nm and 555nm? It would be very interesting to see what those wavelenghts really, truly look like, when they are converted into colored little squares on the screen. For example, when it comes to those who think that the Sun is yellow (which means practically everybody), a colored square corresponding to 555nm might just look a
lot greener than their assumption of "solar yellowness".
As for the discussion of brightness, whether a light grey car looks white or grey, I don't think that sort of discussion is of any interest here. Like Chris said, white and grey is the same color, and it is only the brightness that differs. For the same reason, I don't think that the Moon discussion is really pertinent here. I admit that it is truly fascinating that the Moon is so very dark. Its albedo is only 7%, while the Earth's albedo is around 40%. (And the albedo of Enceladus is close to 100%.) If we are to talk about the
color of the Moon, we have to talk about the subtle differences in hue of various parts of the lunar surface:
Enhanced colors of the Moon.
Finally, I have to comment on something else that Chris said:
BTW, I'll modify what I said earlier. The Sun as viewed from space ought to have a slightly blue cast. It is really sunlight as we see it through the atmosphere that defines "white".
Yes!!! Chris took back something he had said! And he says that sunlight should be thought of as either white or slightly blue! Where is the "jumping up and down with joy" smilie?
Oh, thanks for the figure describing the solar radiation spectrum, Chris!
Ann
[quote="Chris Peterson"][quote="Ann"]Chris, since you are the staunch defender of the idea that the Sun is yellow...[/quote]
Why do you say that? I consider the Sun to be white [/quote]
Wow! Thanks, Chris! I'll hold you to it.
[quote]G stars are called "yellow", a terminology that has nothing to do with their actual apparent color.[/quote]
:roll: :evil: That's the worst kind of astrospeak. The Sun is defined as a G2 star and therefore it is defined as yellow, which does not, however, God forbid, means that it [i]is[/i] yellow!
I'll keep insisting that the whole sorry bit of color definition in astronomy has everything to do with the fact that Vega has, extremely wrongly, been defined as the ultimate example of stellar whiteness. If Vega is white, then all stars yellower than Vega must be either yellow-white, yellow, orange or red. What a pity: when astronomers finally found the "brown" dwarfs, tiny embers of failed stars which emit only a bit of red light and no other visible light, the term "red dwarf" - which should of course have been given to those puny little red-only stellar midgets - had long ago been given to faint yellow-orange stars like Proxima Centauri. (And to add confusion to confusion: Vega is a "dwarf", because it is very much on the main sequence, and it is defined as "white", because it is the ultimate astronomical definiton of stellar whiteness, so it must be a "white dwarf"... except it is anything but a white dwarf, even though it is [astronomical definition]white[/astronomical definition] and it is a [astronomical definition]dwarf[/astronomical definition]. I hate these super-stupid definitions which seem designed to give you the wrong idea about stars!!!)
Back to the Sun. Chris said this about its light output:
[quote]The most intense individual peaks are around 450nm, which looks blue. The blackbody associated with the Sun's temperature, 5800K, has a peak of 500nm, close to cyan. The best fit blackbody to the actual spectrum is 5250K, which has a spectral peak of 555nm, which is the yellow side of green.[/quote]
Does anyone have any actual "color samples" corresponding to 450nm, 500nm and 555nm? It would be very interesting to see what those wavelenghts really, truly look like, when they are converted into colored little squares on the screen. For example, when it comes to those who think that the Sun is yellow (which means practically everybody), a colored square corresponding to 555nm might just look a [i]lot[/i] greener than their assumption of "solar yellowness".
As for the discussion of brightness, whether a light grey car looks white or grey, I don't think that sort of discussion is of any interest here. Like Chris said, white and grey is the same color, and it is only the brightness that differs. For the same reason, I don't think that the Moon discussion is really pertinent here. I admit that it is truly fascinating that the Moon is so very dark. Its albedo is only 7%, while the Earth's albedo is around 40%. (And the albedo of Enceladus is close to 100%.) If we are to talk about the [i]color[/i] of the Moon, we have to talk about the subtle differences in hue of various parts of the lunar surface:
[img]http://www.atalaia.org/filipe/moon/colorofthemoon_files/compare.jpg[/img]
Enhanced colors of the Moon.
Finally, I have to comment on something else that Chris said:
[quote]BTW, I'll modify what I said earlier. The Sun as viewed from space ought to have a slightly blue cast. It is really sunlight as we see it through the atmosphere that defines "white".[/quote]
Yes!!! Chris took back something he had said! And he says that sunlight should be thought of as either white or slightly blue! Where is the "jumping up and down with joy" smilie?
Oh, thanks for the figure describing the solar radiation spectrum, Chris!
Ann