Distance and our eyes distort the true colors of stars

New research calculates the colors of stars based on their actual energy distributions

Hubble / NASA, ESA, and the Hubble SM4 ERO Team

From our perspective on Earth, most stars look like tiny, twinkling dots. But what color would a star be if you could actually see it up close?

Most astronomy textbooks will clearly say hot stars are blue, and colder stars are red. These colors come from an idealized version of the light a star gives off, called a blackbody curve. That’s not quite the whole story though, especially for smaller stars — the outer layers of a star absorb parts of the light emitted from the center, and our eyes respond differently to different wavelengths of light.

New research published in Research Notes of the American Astronomical Society calculated colors of stars based on their actual energy distributions and the response of the human eye. Turns out, we’ve been missing stars’ true colors. The hottest stars appear blue, as we’ve thought, but stars like our Sun appear off-white. Smaller stars, like K and M stars, are beige instead of red.

Most shocking of all — brown dwarfs aren’t even brown, they’re violet! These cool sub-stars are purple because absorption by molecules in their atmospheres takes out a whole chunk of their visible light, leaving only red and blue light for us to see.

There are a few more complexities that could change the color a star appears to us. For example, clouds on brown dwarfs may change how their atmosphere absorbs light, and that’s something researchers are still trying to figure out. Earth’s atmosphere reddens light, too, so all these colors would look different if we were looking from Earth’s surface. For now, though, it’s fun to have a better idea of what vivid colors are out in the universe, including purple (brown) dwarfs!