1. Comets, Asteroids, and Meteors

2. Comets one of the most glorious things to see in the sky is a comet. May be visible for only days, weeks, or months Comet: chunks of ice and dust whose orbits are very long, narrow ellipses. Think of them as a “dirty snowball”

3. Orbits are so elliptical few pass near Earth Comets have… – The nucleus: inner layer – The coma: outer layer of gas & dust – The tail: made of gas & dust, looks like hair Edmond Halley studied orbits of 24 comets – Found same comet appeared every 76 years – Comet named after him (Halley’s Comet) – Appeared last in 1986

4. Asteroids Between 1801 and 1807 astronomers discovered 4 small objects between Mars & Jupiter Over next 80 years found 300 more Asteroids: objects in space to small to be considered planets Asteroid Belt: asteroids revolve around sun between Mars & Jupiter

5. Some asteroids come near Earth One day one might hit Earth 65 million years ago one hit – Made a crater 200 kilometer in diameter – By Yucatan Peninsula – Dust covered light from Sun for months – Caused huge fires and extinction of animals

6. Meteors On average a meteor streaks overhead about every ten minutes Meteoroid: chunk of rock or dust in space Usually come from comets or asteroids When meteoroid enters atmosphere friction causes it to burn up Meteor: streak of light produced by burning meteoroid

7. Some burn all the way up but some don’t Meteorites: meteoroids that pass through atmosphere and hit earth Cause craters (like those on the moon) Meteorites fall all over Earth but most look just like rocks so we don’t notice them