system
Given the following post, respond as if you're commenting on Reddit:
human
Does every celestial body (like Planets, stars, satellites, nebula etc) always rotate around their axis? Why do they rotate?
gpt
Generally, yes. Basically, it's just extremely unlikely that the gas that formed the star or galaxy or whatever happened to have exactly zero angular momentum - every flow of gas would have to be perfectly balanced by some other gas moving in the opposite direction, and that's not going to happen very often. For galaxies and stars, this just comes from the random turbulent motions of the gas. But things like planets and moons form within rotating discs, so there's going to be some angular momentum naturally flowing into them - that's why all the planets rotate the same way that they orbit. This doesn't happen for stars because star forming regions are tiny compared to the size of the galaxy, so random turbulence matters more than the large-scale rotation of the galaxy. But planets are reasonably large compared to the size of the solar system, so the rotation of the star-forming disc dominates.