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I hope they point it at the night sky and see a green star. That would be a very exciting event, as naturally green stars are not possible. I know that if I w

I hope they point it at the night sky and see a green star. That would be a very exciting event, as naturally green stars are not possible. I know that if I was an advanced "angler fish" type of civilization, that's definitely the lure I would use in a dark forest universe. on that note i hope the scientists are not stupid enough to send a signal to that star.

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poulpy123 2y ago
Why would they detect a green star ?
amenghra 2y ago
Some stars, eg Lambda B, do appear green when looking thru amateur telescopes.
- adrian_b 2y ago
  Most likely they appear blue-green (a.k.a. turquoise a.k.a. teal), not green. As another poster has mentioned, with increasing temperatures the color sequence for a black body is black => red => yellow => white => blue-green => blue. Neither the greenish colors intermediate between yellow and blue-green nor the purplish colors intermediate between red and blue can appear as colors of a hot body, but only the colors that can be seen when low-pass filtering white light (i.e. between red and yellow, inclusive) or when high-pass filtering white light (i.e. between blue-green and blue, inclusive). While above I have simplified by saying that purplish colors should not appear, that is only partially true, because very hot stars could appear as violet, i.e. reddish blue, due to the defect of human vision that the red photoreceptors are sensitive not only to red light, but also to light with a higher frequency than where the maximum sensitivity for blue is, so the high-frequency violet light excites both the blue and the red photoreceptors, being indistinguishable from a mixture of blue light with low-frequency red light. With a video camera where the output signals would not be processed in such a way as to mimic the bugs of human vision (like in all normal color video cameras), purplish colors would not be obtained for hot bodies.
  - amenghra 2y ago
    When you have double (or more) stars and gases involved, you can end up with a green-ish tint. Obviously, different people will describe the color in a different way due to everyone's own seeing conditions, instruments, and color sensitivity.
    - adrian_b 2y ago
      Oxygen has a strong green emission, so gases rich in oxygen may appear green, which is why many nebulae are green, like also most auroras in the Earth's atmosphere. Therefore indeed a star behind gas rich in oxygen may appear green, but that green light comes from the gas, not from the star.
hnuser123456 2y ago
It's not really possible to make a green star because the color is mostly just determined by the temperature, with colder stars being redder and hotter being blue. A green star would just be a white star, or a star with the same temperature as the sun, whose peak output is in the green range, but having almost equal amounts of light in the blue and red range, appearing white. There is no way to "squish" the black body spectrum into a narrower range, it is determined by the Maxwell–Boltzmann distribution of velocities of particles in a gas.
- nowittyusername 2y ago
  That's my point. A green star would signal to anyone in the universe that something is really off here and most likely achieved by unnatural means (aka and advanced civilization). This would attract attention. which the civilization that sent the beacon can take advantage of for various reasons. There are many such beacons that could be placed all over the universe to attract attention.
  - hnuser123456 2y ago
    I see what you're getting at. My thoughts on that topic are... it would be really hard to make a recognizable signal that crosses a significant fraction of the universe, or even galaxy. There could be a laser-pointer-green sun on the other side of the Milky Way, but a single sunlike star is already impossible to detect on the other side of the galaxy, much less in another galaxy. 95% of the brightest stars in the sky are less than 1000ly away, while the galaxy is 100,000ly across. The ones that are over 1000ly away and still visible are extremely large, unusual stars. R136a1 is one of the brightest stars known, at almost 5 million times the luminosity of the sun, it's just outside the Milky Way in the LMC, and it required 3.6 meter telescopes to tell that it was multiple extreme stars around a single, very extreme star. In any telescope picture where R136a1 is visible, a regular sun-like star in the vicinity would be invisible. There are no images of "normal" stars more than 1000ly away because they just combine into an ambient glow of space. The amount of energy needed to broadcast a signal to the entire galaxy (much less universe) requires something like a supernova, which... just looks like a supernova. https://en.wikipedia.org/wiki/R136a1 https://en.wikipedia.org/wiki/R136a1

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poulpy123 2y ago

Why would they detect a green star ?

amenghra 2y ago

Some stars, eg Lambda B, do appear green when looking thru amateur telescopes.

adrian_b 2y ago
Most likely they appear blue-green (a.k.a. turquoise a.k.a. teal), not green. As another poster has mentioned, with increasing temperatures the color sequence for a black body is black => red => yellow => white => blue-green => blue. Neither the greenish colors intermediate between yellow and blue-green nor the purplish colors intermediate between red and blue can appear as colors of a hot body, but only the colors that can be seen when low-pass filtering white light (i.e. between red and yellow, inclusive) or when high-pass filtering white light (i.e. between blue-green and blue, inclusive). While above I have simplified by saying that purplish colors should not appear, that is only partially true, because very hot stars could appear as violet, i.e. reddish blue, due to the defect of human vision that the red photoreceptors are sensitive not only to red light, but also to light with a higher frequency than where the maximum sensitivity for blue is, so the high-frequency violet light excites both the blue and the red photoreceptors, being indistinguishable from a mixture of blue light with low-frequency red light. With a video camera where the output signals would not be processed in such a way as to mimic the bugs of human vision (like in all normal color video cameras), purplish colors would not be obtained for hot bodies.
- amenghra 2y ago
  When you have double (or more) stars and gases involved, you can end up with a green-ish tint. Obviously, different people will describe the color in a different way due to everyone's own seeing conditions, instruments, and color sensitivity.
  - adrian_b 2y ago
    Oxygen has a strong green emission, so gases rich in oxygen may appear green, which is why many nebulae are green, like also most auroras in the Earth's atmosphere. Therefore indeed a star behind gas rich in oxygen may appear green, but that green light comes from the gas, not from the star.

hnuser123456 2y ago

It's not really possible to make a green star because the color is mostly just determined by the temperature, with colder stars being redder and hotter being blue. A green star would just be a white star, or a star with the same temperature as the sun, whose peak output is in the green range, but having almost equal amounts of light in the blue and red range, appearing white. There is no way to "squish" the black body spectrum into a narrower range, it is determined by the Maxwell–Boltzmann distribution of velocities of particles in a gas.

nowittyusername 2y ago
That's my point. A green star would signal to anyone in the universe that something is really off here and most likely achieved by unnatural means (aka and advanced civilization). This would attract attention. which the civilization that sent the beacon can take advantage of for various reasons. There are many such beacons that could be placed all over the universe to attract attention.
- hnuser123456 2y ago
  I see what you're getting at. My thoughts on that topic are... it would be really hard to make a recognizable signal that crosses a significant fraction of the universe, or even galaxy. There could be a laser-pointer-green sun on the other side of the Milky Way, but a single sunlike star is already impossible to detect on the other side of the galaxy, much less in another galaxy. 95% of the brightest stars in the sky are less than 1000ly away, while the galaxy is 100,000ly across. The ones that are over 1000ly away and still visible are extremely large, unusual stars. R136a1 is one of the brightest stars known, at almost 5 million times the luminosity of the sun, it's just outside the Milky Way in the LMC, and it required 3.6 meter telescopes to tell that it was multiple extreme stars around a single, very extreme star. In any telescope picture where R136a1 is visible, a regular sun-like star in the vicinity would be invisible. There are no images of "normal" stars more than 1000ly away because they just combine into an ambient glow of space. The amount of energy needed to broadcast a signal to the entire galaxy (much less universe) requires something like a supernova, which... just looks like a supernova. https://en.wikipedia.org/wiki/R136a1 https://en.wikipedia.org/wiki/R136a1