­ Q: Why do comets have tails? A: The comet's dust tail is made of small (one micron) dust particles that have evaporated from the nucleus.The dust tail is the easiest part of the comet to see because it's long and reflects sunlight. Comets often have a second tail called an ion tail. The ion tail is made of electrically charged gas molecules that solar wind pushes away from the nucleus.

­ Comets have fascinated mankind since humans first noticed the distinctive tail streaking across the night sky. We mark the date that we sa­w a comet that comes around only once a century or even once in four centuries and we remember the sight for the rest of our lives. Astronomers find comets fascinating, too. Comets are remarkable pieces of our universe's past, and they tell us a great deal about how the universe was formed.

Almost every year, we are visited by comets from the outer reaches our solar system. Most recently, comet LINEAR rounded the sun and broke apart. In this edition of How Stuff Works, we will examine the fascinating world of comets. We will find out what comets are, what they are made of, where they come from and how to observe them. You can learn where to look for comets and maybe even discover one yourself!

Comet Image Gallery