9 billiard balls, which one is heavier/lighter?

Question

This is a variation of the microsoft trivia.

You have 9 billiard balls, and a weighing balance. 8 balls weigh the same. The other ball is either heavier or lighter. What's the fewest number of times you'd have to use the balance to find out which ball is different, and if it is heavier or lighter than the others.