To contact the spirit of the previous Avatar, Aang must reach a temple in the Fire Nation before the sun sets on the following day. There he will learn what he must do to restore balance to the world. Zuko must defy his banishment to follow Aang.
Did You Know?
A comet is made of ice and rock, so it couldn't give Firebenders any power. That's true in our world, but the Avatar world is very different in terms of physics and reality (since when can people shot fire out of there arms). So the comet could actually be made of fire or some chemical that makes the Fire nation more powerful. See more
Let's go, Appa. Come on, boy. Look, I'm sorry, but Katara and Sokka aren't coming to the Fire Nation with us. If they got hurt, I'd never forgive myself. So get your big butt off the ground and let's go!
[Appa remains on the ground
I think his big butt is trying to tell you something.