Super Mario Galaxy/Beach Bowl Galaxy

Beach Bowl Galaxy is accessible from the Kitchen observation dome. You need 16 Stars to enter.

Star 4 (Fast Foe Comet): Fast Foes on the Cyclone Stone
This Star is available when a Prankster Comet is in this Galaxy.

Do the same as for the last section of Star 3, except with faster moving platforms and Thwomps. Luckily there are no Goombas this time.

Star 5 (Purple Comet): Beachcombing for Purple Coins
This Star is available when a Purple Comet is in this Galaxy.

You need to collect all 100 Purple Coins, with no time limit.