Comets

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

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

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.

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.

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

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

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

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.