Summary:

- Meteor showers occur when the Earth passes through debris left behind by comets. These debris particles burn up in the Earth's atmosphere, creating the "shooting stars" we see.

- Some meteor showers, like the Perseids, are very predictable and happen around the same time each year. Others, like the Leonids, are more unpredictable and can vary in intensity from year to year.

- The unpredictability of some meteor showers is due to the way the debris is distributed in the comet's orbit. Factors like the comet's size, the speed of the debris, and the way the debris is spread out can all affect how intense a meteor shower will be.