The UV sun radiation (shorter than 300 nm) is absorbed by atmospheric O3 and O2 molecules. The latter also absorb in the red spectrum range (Atmospheric absorption bands, 540-770 nm). In the IR range CO2 and water absorb strongly.

Thank you Yuriy, for your reply!

Do you know, if the fusion generated light in the sun's core is UV or visible radiation?

Nope. Basically, fusion reactions produce gamma rays. These photons scatter many times against the charged particoles in the Sun's core, and each collision may producephotons of lower frequency. After many collisions, they escape. When they escape, they are noi more gamma photons, but X, UV, light, infrared etc. It takes about one million years for a photon to escape from the core to the external layers of the star; then it takes just 8 minutes for the photon to travel up to Earth.

Thank you, Andrea, for your reply!

Is the slow movement (1 million years) also true for the secondary light photons, or only for the gamma rays?

Is there a special order of frequencies following a collision (like: halving of the primary frequency or doubling of the wavelength or whole number ratios between primary and seconary photos)?

Dear Maximilian, AFAIK the figure of one million years holds for the overall process made of many emissons, absorpions, emissions again etc. from the core (where fusion occurs) and the final escape towards Earth. Various collisions occur; however, since the energy of a gamma photon is larger (MeV) than the typical energy of the charged particles it intreacts with (tens of KeV), each collision induces a slight decrease of the photon energy (more precisely, at each interaction at least one photon is destroyed and one photon is created, the energy of the created photon being slightly smaller than the energy of the destroyed photon). Conservation of energy dictates that the charged particles are given the amount of energy lost by photons, and get heated. Of course, the exact amount depends on the initial momentum and energy of both the photons and the charged particles involved in the interaction. However, the relative smallness of the amount of energy lost by photons at each collision is due to the fact that the rest mass of the charged particles (equivalent to hundereds or thousands of Mev) is much larger than the photon energy (MeV): it is like a tennis ball hitting a locomotive, the ball gets scattered with almost all of its initial energy and the locomotive is given just a tiny amount of energy. This smallness is the reason why it takes so many collisions to decrease the photon energy down from the MeV values of gamma photons to the fraction of eV of infrared and light.