(ORDO NEWS) — Star cluster NGC 4755 is often referred to as the Jewel Box because its stars look like sapphires with rare rubies and diamonds in a small telescope.
However, there are no emeralds. And it doesn’t just seem that way. It turns out that there are simply no green stars in space.
To the naked eye, at least to most people, stars appear red or white. When telescopes are used to increase the brightness, some of these seemingly white stars turn orange or blue, and some may turn yellow.
The absence of stars of the central color of the rainbow does not indicate a gap in the physical properties of the stars, but about the features of perception.
Most of the colors that can be seen on Earth are due to the surface chemistry of objects, which determines which wavelengths of light are reflected and which are absorbed. However, the stars are different. Their color depends on temperature.
Cool stars (3700 Kelvin and below) emit light mainly in the red part of the spectrum (longer than 625 nanometers), as well as in the infrared range invisible to us.
Unlike our associations of blue with cold and red with hot, when stars heat up, they emit shorter wavelengths of light, which is why the hottest stars, like Sirius, appear completely blue.
The relationship between maximum temperature and wavelength is determined by the Wein displacement law.
According to his formula, a 5500K star will emit a maximum of 527 nanometers of radiation almost in the center of the green part of the spectrum.
The absence of green stars now seems even more mysterious. Stars of this temperature certainly exist – after all, the photosphere of the Sun, which determines their light, is not far from the temperature of 5.72 K – so why are they not green?
The key point in the answer is that stars do not only emit light at the top of their shape, like a string producing sound of one wavelength.
A peak is just a peak, stars always produce many longer wavelength photons and a few shorter wavelength photons.
If our eyes were only focused on the maximum wavelength, we would see that stars like the sun appear green but behave differently.
When we encounter a mixture of green and yellow to which red and blue are added, we see this mixture as white.
We observe the same process when an object on Earth is heated. It first glows red, then orange, then white. If we have a strong enough heat source, it may even glow blue, but not green.
We can see green stars if we pass light through a filter that cuts off other wavelengths, but this is actually just a hoax. However, the universe has a few tricks up its sleeve.
Popular optical illusions cause us to look at multi-colored shapes and see contrasting eerie remains after we look away as our eye cones get tired of being overloaded with color. Celebrities can do the same.
Antares is a star so bright and red that its name literally means “rival of Mars” (Greek “Ares”). His much weaker companion, Antares B, is white.
However, when viewed in the same field of view, Antares B appears green for contrast. Similar descriptions have been given for other white satellites of brighter red stars.
Grass or living leaves appear green to us because that is almost the only wavelength of sunlight they reflect back to us. Some objects in space are similar, such as a rare green comet.
In addition to the smooth curves of heat emitters, like the Sun, individual elements emit certain spectral lines due to the energy transitions of their electrons.
Some of them, such as calcium, especially stand out in green. However, other colors of light are usually enough to create an overall white effect, as long as the light is not broken down into its components.
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