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What could make a star green?
- Rooster61 10y agoWe can never perceive a green star with our eyes alone without some sort of substrate between the two blocking the red and blue light emissions. This is because green falls smack dab in the middle of the visible light spectrum. When a star a appears blue, most of what is being emitted by the star is photons with a frequency that appears blue, and photons with a frequency of ultraviolet or higher. Same goes for red stars, except instead of ultraviolet, it emits frequencies in infrared and lower, resulting again in light that our eyes cannot pick up. We only see the red photons that our eyes are able to pick up. If we could see further into the ultraviolet and infrared spectrum, "blue" and "red" stars would most likely disappear in favor of whatever colors blue+ultraviolet and red+infrared look like. This is what we see when we look at a white star. It's a star emitting most of its light in the green spectrum, but also emitting reds and blues, thus appearing white. (Fun side note: Our sun is actually what a "green" star would look like if we could actually see them. It's white when viewed from space. It only changes colors and appears primarily yellow due several factors affecting the photons in our atmosphere. Absorbption of certain wavelengths, Rayleigh scattering, ect.)
- dhimes 10y agoWe can never perceive a green star with our eyes alone without some sort of substrate between the two blocking the red and blue light emissions. A doppler shift of a red or blue star would do it.
- empath75 10y agoNo. A stars spectrum is spread out. Stars that look red or blue are mostly in infrared or ultraviolet. If you doppler shifted it to the middle of the visual spectrum, it would look white, not green.
- wolf-rayet 10y agoThe spectra of Wolf-Rayet stars are characterized by bright emission (rather than absorbtion) lines. Maybe you could get something that looks more-green-than-not to human eyes with the right red- or blue-shift of the right WR star?
- Rooster61 10y agoHow so? A doppler shift would only shift the apparent wavelengths that are already present. For it to create a green star effect, it would need to actively remove the upper and lower ends of the star's spectra.
- kmm 10y agoBlack-body radiation has the interesting property that it is invariant under redshift. I.e. a redshifted black body spectrum stays a black body spectrum, but for another temperature
- andrewflnr 10y agoIs black-body the only spectrum for which that's true, i.e. could you (in principle) define it that way?
- kmm 10y agoNo, it's true for any spectrum which is a function of the ratio of frequency and temperature, as we can then shuffle the factor appearing due to redshift into the temperature. Apart from any constant prefactors, because those don't change the shape of the spectrum but just its absolute value.
- dhimes 10y agoAck! I can't edit so I'll say here- you guys are right. My mistake. :(
- jstanley 10y ago> You cannot [...] Says who? This StackExchange is for people writing fiction. They can do whatever the hell they want. It's fine to advise against certain things that might detract from credibility, but telling people they "cannot" do things comes across awfully self-important. EDIT: Maybe I'm getting downvoted because of the self-importance of telling people they cannot tell people that they cannot do things? :)
- JMStewy 10y agoIt's the asker saying "you cannot," likely because of decisions he or she has already made about the setting and characters of the story that the green star will be in. Your response would only make sense if it were an answerer trying to tell the asker what he or she cannot do.
- jstanley 10y agoAh, I see! I understand now. I thought this was a link to an answer, and I thought the question was merely "What could make a star green?" Starting out with a bold "stars are never green" and then explaining why made it seem to me more like an answer than a question, and the brief questions seemed rhetorical.
- pjc50 10y agoWorldbuilding.SE is weird. People are very unclear whether they want "plausible fiction" or "hard science" answers for things, and to some extent it's also treated like a puzzle - which I think is what the phrasing means here. "You may/may not" phrasing appears in exam questions.
- acbabis 10y agoThis hasn't been my experience. Worldbuilding has hard-science and soft-science tags, and the better posts use them. Puzzle questions tend to get flagged and closed.
- arethuza 10y agoAs an aside: there is a rather splendid explanation for stars going green in Ken MacLeod's SF novel Learning the World: https://en.wikipedia.org/wiki/Learning_the_World https://en.wikipedia.org/wiki/Learning_the_World
- scrumper 10y agoArgh I'm halfway through Absolution Gap now, and there's a quote from the bloody epilogue halfway down the page! Managed to avoid reading most of it fortunately.
- the8472 10y agoWould dumping enough copper into the star work or would that still glow white?
- marcosdumay 10y agoIf you spread enough of it around the star, sure, it will do. But into the star won't help you.
- jccalhoun 10y agoenvy?
- hencq 10y agoCompletely unrelated, but the green stars reminded me of the chapter from Surely You're Joking Mr Feynman where he's judging math books [1]: > Finally I come to a book that says, "Mathematics is used in science in many ways. We will give you an example from astronomy, which is the science of stars." I turn the page, and it says, "Red stars have a temperature of four thousand degrees, yellow stars have a temperature of five thousand degrees . . ." -- so far, so good. It continues: "Green stars have a temperature of seven thousand degrees, blue stars have a temperature of ten thousand degrees, and violet stars have a temperature of . . . (some big number)." There are no green or violet stars, but the figures for the others are roughly correct. It's vaguely right -- but already, trouble! That's the way everything was: Everything was written by somebody who didn't know what the hell he was talking about, so it was a little bit wrong, always! And how we are going to teach well by using books written by people who don't quite understand what they're talking about, I cannot understand. I don't know why, but the books are lousy; UNIVERSALLY LOUSY! [1] http://www.textbookleague.org/103feyn.htm http://www.textbookleague.org/103feyn.htm
- astrobe_ 10y agoIf there's a redshift, there might be a greenshift?
- antisthenes 10y agoIn a non-Euclidian geometry perhaps.
- Pica_soO 10y agogreenfly
- based2 10y agohttps://en.wikipedia.org/wiki/Planck%27s_law https://en.wikipedia.org/wiki/Planck%27s_law