Is the yellow color really yellow

Yellow, red, white? Researchers have calculated the colors of stars

  • The astrophysicist René Heller dealt with the question of the color of stars, as reported by "Spektrum".
  • Since the human eye cannot capture a spectrum with an infinite number of wavelengths, the human eye's color perception was calculated using computer-generated star spectra.
  • The result: there are no green stars. There are also no stars with the color cyan, purple or yellow - therefore no yellow sun either.

Due to atmospheric effects, we usually perceive the sun as yellow - and at dawn or dusk it often appears red or orange. In fact, it is white, just as the red giant star is not red and the white dwarf is not white. What color are stars then? The astrophysicist René Heller from the Max Planck Institute for Solar System Research in Göttingen dealt with this question, as reported by "Spectrum".

The color of a star depends on its surface temperature, provided it is a perfect blackbody radiator. This means that the radiation that hits a star penetrates deep into it and is hardly reflected. “In general, the stronger a body emits the more light it absorbs,” explains physicist Dietrich Zawischa from the University of Hanover. A black body glows the brightest and, depending on the temperature, emits light in all wavelengths. The hotter the star, the shorter the wavelength.

This also explains why the sun should be white: As a black body radiator, it emits light in all wavelengths. In contrast, smaller stars are cooler and therefore more reddish and larger stars are blue due to a temperature that is many times higher than that of the sun. However, this calculation does not necessarily describe what we humans see with our eyes.

The sun is almost white with a slight orange tinge

Using models, Heller and the student Jan-Vincent Harre from the University of Göttingen tried to determine this so-called color valence of the stars. Their results appeared in a specialist article. So they calculated what color the stars are to the human eye - because the human eye cannot capture a spectrum with an infinite number of wavelengths.

Color perception is usually represented by three numerical values ​​for the three colors red, green and blue. It turned out that the sun is actually almost white, but has a slight orange tinge. In the sun's color space, there is a little more red than blue and green. In contrast, cooler red dwarfs are more likely to be perceived as orange by the human eye. This is because their stellar atmospheres absorb some of the red light. Blackbodies don't do that.

The metallicity of a star also affects its color. Metallicity is understood as the abundance of elements in a star's atmosphere that are heavier than hydrogen and helium. However, the differences could not be seen with the human eye, at most they could be calculated with a computer. Heller and Harre come to another conclusion: there are no green stars. Neither are there any stars with the color cyan, purple or yellow - therefore no yellow sun either.