No such thing as green stars?

[Buttercup]

I do recall reading about GREEN stars in an astronomy book (geared for younger readers) when I was a kid.

Lo and behold, now supposedly there is no such thing as a green star. Supposedly because no combination of gases could produce one. :-\

Is this true?

Because I'd really like to think there are green stars out there.

[antoniseb]

It is plausible that there is some L-Dwarf with the right chemistry in its atmosphere that it could look green, but what you think of as (between yellow and blue temperature) green would be white.

[Tog]

This is my understanding of it.

It's not that no combination of gasses can make green, it's all about temperature. When something is hot enough to glow in the visible spectrum, it starts off red, then goes to white, then blue. The reason it's white is because it isn't one colot like a neon sgin or a laser, but a whole range of them that peaks at the color we call it. A "red" is mostly infra-red, then some red and some orange and yellow. We can't see the infra-red, so see wee the second most dominant color. The red. It washed out the yellow and orange.

For a start to be green, it would radiate almost the entire visible spectrum as its range. When you add all those colors together, you get white. This is compounded by the fact that human eyes or not all that sensitive to green light as compared to the other colors.

See below for corrections.

[Rhaedas]

Plus, isn't green a very small section of the visible spectrum, compared to other colors? One reason why the green flash of sunsets is an uncommon event, because the conditions have to be good enough to allow that part of the spectrum to show long enough for it to register. So for a star to put out just a green light would be practically impossible, because there are so many wavelengths given out in the reactions. And as said, generally those combinations appear to us as a white color, unless we separate them out.

[Hornblower]

When I project sunlight with a prism, I see a broad band of red shading to orange, a very narrow band of yellow, and a broad band of green shading into a broad band of blue, with a vivid violet at the far end. That is a close approach to a blackbody spectrum, and our eyes are adapted to perceive the blended mixture as white.

Some observers have reported a greenish tinge to white stars that are barely bright enough to stimulate any color vision at all. This phenomenon could have been misdescribed in a poorly written kiddie book. If we make them enough brighter to make all of the cones function, they simply will look white unless seen in contrast with red or magenta ambient light, or in contrast with a reddish and brighter binary companion in a close double star.

[John Reed]

This was my first question on the BAUT forums. Some more answers:

http://cosmoquest.org/forum/showthre...t=#post1809494

[Ara Pacis]

This explains why the Green Lanterns are so rare.

[Romanus]

Everyone has explained this fairly well. The only stars that really look green are ones that are juxtaposed with another star of different color (that is, temperature); Antares's companion has often been described as green, as is the companion of Epsilon Bootis (Izar). However, both stars are "technically" blue and white, respectively; it's only an optical illusion that makes them greenish.

[Shaula]

Ah ha! Been driving me nuts, I knew I remembered one star as being describes as naked eye green: Beta Librae. May have to have a look at that later. I remember reading that it was greenish years ago and been looking for the name of it ever since!

http://earthsky.org/brightest-stars/...nly-green-star

[chrlzs]

Also, my Collins Guide to Stars & Planets lists one of the stars comprising the double of Beta Cygni (Albireo) to have a blue green colour. Given my (mild) colorblindness, I shall not comment..

[Shaula]

Actually a quick flick through the Collins Gem guide and they list a few stars as blue-green.
Alpha Herculis's companion
Beta Cygni's companion
32 Eridani's companion
Alpha Scorpii's companion

As has been said though, colour determination by eye in double stars is a complicated thing. I think all of them are companions to red/orange stars - which may explain it.

[Nick Theodorakis]

The Albireo companion always looked blue to me, but I guess your mileage may vary. Both Phil and Fraser have written on this:

http://www.universetoday.com/25152/a...e-green-stars/
http://blogs.discovermagazine.com/ba...o-green-stars/

Nick

[Buttercup]

The Albireo companion always looked blue to me...

Me too. Very much so. And speaking of which (now in night-time sky). :-)

I have a book (reprinted edition) which asserted there are green stars. Will get that out of closet Sunday or Monday.