If you're actually played this game, you probably know that sometimes stars are hidden (more or less) between the constellations.
Everytime you click on a new of those a info-window appears.
If you equalize the waves, a green fast-forward thingy pops up and if you click on it you get your achievement.
So the catch is, the stars are random and you can get a lot of them at level seven.
Just repeatedly play the level to get them all. There is no need to finish the level.

That's all, happy hunting!