Have you heard of Halley's comet? It has made an appearance in Earth's solar system at around 76 year intervals for more than 2000 years! Do you know that you can actually see the orbit of the comet as it moves slowly across the sky, goes behind the sun, and appears again? This huge, dirt-filled snowball can't be seen when it starts the long journey at the edge of the solar system until the sun reflects off of it, just like the earth and the moon. Its long tail stretches across many millions of miles of the night sky as it is pushed away from the sun by the solar wind. Although the comet appears to be on fire, when its glowing tail passed over Earth in 1910 no one was injured. Some passing comets with longer orbits may not be seen again for hundreds of years and some never return. Would you like to have a space object named after you? Comets are usually named after the first person that discovered them. If you want to find your own comet, scan the skies and look for a fuzzy patch of light that seems to be in a slightly different area of the sky each night. Many stargazers have found comets with nothing more than a pair of binoculars! If you just want to look at one that someone else has discovered, ask your family to let you know when a comet is scheduled to appear again. They can help you keep track of them and the other interesting events by reading astronomy magazines or checking http://skychart.skytonight. com/observing/skychart/skychart.asp on the Internet. The first time you visit this site you may need an adult to help you type in your location and time zone. (If you would rather use another site, that would be fine too.)

Confusing Comets

This astronomer is searching for a special comet, but there seem to be a lot of choices!Which is the one he wants? Use the clues to find out!

The correct comet…

…must have 4 tails

…must have the tails on the left side

…must be round

…must be smooth

Out of This World

Imagine that you could take a ride on Halley's comet. You know that it circles around the sun, but where would you be going on the return trip? You would have to travel billions of miles from the sun, past Neptune, to the source of most of the short-period comets. You might think your destination would be Saturn's rings that are shaped like a plate and filled with thousands of icy snowballs known as Kuiper's Belt Objects. Many astronomers wonder if icy Pluto and many of the moons orbiting the gas planets came from here. Have you ever wondered why the comets started their journey? A planet's gravity may have tugged on them if they got too close or the comet could have been struck by debris passing through space. Your trip wouldn't stop here if you were riding a long-period comet. They take hundreds, some of them millions, of years to orbit the sun so you could travel trillions of miles to the edge of the solar system! You'd be traveling to the Oort cloud, which encircles the solar system completely. Its comets can come from any part of the sky, not just from one direction like shorter-period comets do. You won't see the Oort cloud on the Solar System Viewer on the Internet, because no one has really seen it, even with a telescope — astronomers just know it's there!Be sure to check out the other orbiting objects in space. Even though the solar system is really big, some of these things look like they come pretty close to each other! Do you think as the universe expands or contracts that it will effect the orbits or courses of all these objects?