#orbits
The path a star or planet takes round what holds it. A shader that knows the orbit doesn't need to move a particle a step at a time: where it is at any moment is a function of the clock, an angle that grows at the orbit's rate. In a galaxy the rate comes from the rotation curve: a star's speed along its orbit rises through the core and then stays about the same, so the inner stars go round in far less time than the outer ones.
1 shader
