Question

why sun release UV rays?

Answer 1

Sun doesn't release uv rays as it is realised by solar system uv rays are very harmful

Answer 2

The sun is very hot so it emits radiation at many different wavelengths. The surface can be approximated as a blackbody at 6000 K. A normal orange flame may burn at 600 K or so. It isn't hot enough to radiate UV rays but it does radiate in the visible and infrared parts of the electromagnetic spectrum