Is the sun really green?

Why the sun is actually green

One of the milestones for star observation was the radiation law formulated by the German physicist Max Planck in 1900. It describes the relationship between the temperature of a body and the wavelength of the light it emits: the higher the temperature, the higher the energy and the shorter the wavelength of the light. With this law, astronomers and astrophysicists were able to use the light spectrum and thus the color of a star to determine its surface temperature. When it comes to stars, however, astronomers do not speak of colors, but of spectral classes, which are denoted by the letters O, B, A, F, G, K and M.

Today we know that the temperature of the sun's surface is around 6,000 degrees Celsius. This corresponds to yellowish light. However, there are also stars that are significantly cooler at 3,300 degrees and therefore emit red light. Betelgeuse, one of Orion's shoulder stars, is such a shimmering red star. A little warmer is the star Arctur, the brightest star in the Bear Guardian constellation, from which orange light emanates.

Sirius is hotter than the sun, next to the moon, Mars, Jupiter and Venus the brightest phenomenon in the night sky. At around 10,000 degrees Celsius, it shimmers whitish. The hottest stars finally reach temperatures of over 25,000 degrees Celsius and emit a bluish light. However, they emit a considerable part in the ultraviolet range of the spectrum that is invisible to the human eye.

The stars in the sky shimmer from deep red to orange and yellow to white and blue. However, one spectral color is missing: there are no green stars. The reason for this is that the spectra of the stars are very broad. This means that they have a maximum at a certain wavelength, but the intensity drops only slowly to the right and left of this peak. If this maximum is in the green area of ​​the spectrum, the star emits not only green light but also almost as much red, yellow and blue light. The human eye perceives this mixed color as white. The sun is such a star. It would have a green shimmer if this additive color mixing effect did not exist.