What does a supernova look like when it explodes?

When a supernova exploded, the brightness suddenly increased by tens of millions or even hundreds of millions of times, and gradually dimmed after a few months. The violent explosion threw most of the star material into the surrounding space and became a diffuse nebula. 1054 (the first year of the Song Dynasty), astronomers in China discovered and recorded the explosion of a supernova in detail. According to the position recorded at that time, it coincides with the position of the famous Crab Nebula when we see Taurus now. This nebula is still spreading out at a very fast speed. Judging from the speed of its outward diffusion, it initially spread outward from the center, which is equivalent to the time when this supernova explosion was observed in China history books. So now astronomers think that the crab nebula is formed by the material ejected by this supernova.