Because you start each game with only four lives (after shutting the game off and turning it back on), you might be in need of some extra lives upon rebooting the game. You can usually get five right off the bat from Toad (he'll run around with a letter above his head, symbolizing a letter from either Luigi, or more likely Peach). There are four more strewn around the Observatory that you can acquire, however:

1. On the moving green platform below the core.
2. Under the stairs leading to the kitchen.
3. Right at the top of the observatory.
4. Underneath the entrance to the gateway to the stars.