This is a really good effort. I would have liked some sound effects, and I felt as though the star was kind of fiddly to control to begin with - it's very floaty and it seems as though you can only really add momentum in one direction (of four) at a time - but the idea is a a good fit for the theme and I'm impressed by the variety of bullet hell attacks. The sun's "follow you with a beam for a bit before locking it in place and shooting" one is especially good.
If you were to do more with this I'd LOVE to see the two bosses used to defeat one another. You could goad the sun into firing that beam at the moon, and get the moon's homing shot to hit the sun. I found myself trying to do it anyway just for fun.