The second green star in Fleet Glide Galaxy is near the end behind a giant, purple pillar on the left side of the course. You have to hold back and wait for the pillar to fall over before you can get the star.

The third green star in Clockwork Ruins Galaxy is all the way at the end ot the level, and you have to run on top of those giant spinning cog-looking things. Run on top of it until it's about to fall off the ledge, and then long jump off of it to grab the star. You should definitely take a look at the star using up on the Control Pad before getting on any of the cogs, though, so you have a good idea of where to aim.