1. Comets

2. Oort Cloud The Oort cloud surrounds the Sun beyond the Kuiper Belt.
10,000 to 100,000 AU
1/5 the way to the nearest star
Spherical shell of icy objects

3. Cometary Orbits
Comets that are pulled toward the sun enter new orbits.
Nudged by gravity
Most pass only once – never return
A few enter elliptical orbits

4. Comet Nuclei
Comet Halley has a nucleus with a lot of carbon soot and grains of sand mixed with ice.
Comet Borrelly shows gases coming from the surface.

5. Tails As a comet is heated near the sun the ice vaporizes.
The vapors form a coma around the nucleus.
Part of the gas streams away from the sun and forms a tail.
Comet tails can be millions of kilometers long.

6. Meteor Showers Many times each year meteors will arrive in a group.
Up to hundreds per hour
Same direction from space
This is called a meteor shower.
Gary W. Cronks Comets and Meteor Showers

7. Radiant
In the 1800’s astronomers realized that meteors from a single shower came from a single point among the stars.
The point origin is called the radiant.
Named for the constellation in which it appears to originate

8. Repeating Showers Some meteor showers recur at regular intervals.
Leonids match comet Tempel-Tuttle
Astronomers recognized that this was consistent with a predictable orbit.
Orbit of the Leonids

9. Meteor Storms
As comets pass the sun they can leave a large amount of debris.
If the earth hits this debris it can generate 1000’s of meteors per hour.
This is called a meteor storm.