In Class:
Question to Ponder
A comet with a 125 year period has a semi-major axis of 25 A.U. How
far from the Sun does such a comet ever get?
- a) 5 A.U.
- b) 11.2 A.U.
- c) 25 A.U.
- d) 50 A.U.
- e) 125 A.U.
What Are Asteroids?
- They're minor planets, like comets, in that they orbit the Sun
independent of any other planet.
- Unlike comets, they're made mainly of rock and metals.
- Therefore, they don't create the big comas and tails when they're
in the inner solar system.
- That makes them hard to see.
The Asteroid Belt
- Home to most of the asteroids.
- Located between the orbits of Mars and Jupiter (2-3.5 A.U.)
- Analogous to Kuiper Belt -- home of iceballs and short period comets.
- Probably contains 40,000 asteroids with diameter > 1 km.
- Though it contains a large number of asteroids, this region is not at all
crowded -- typical separation between asteroids is greater than 10 times the
Earth-Moon distance.
- "Kirkwood Gaps" are regions within the asteroid belt where, due to the
gravitational influence of Jupiter, stable asteroid orbits are not possible.
- Asteroids move out of these regions, leaving gaps with no asteroids.
Meteors
- bright, short-lived flashes
- upper atmospheric events -- only 30-50 miles above you.
- small amounts of material superheated by friction in upper atmosphere.
- typical size: a penny or smaller.
- occasional "fireball" or "bolide" might be the size of a softball.
- frequency of about 1-4 per hour on a typical night.
Meteor Showers
- Occurs when Earth passes through the trail of a comet.
- Increase in the amount of junk falling onto the atmosphere.
- Showers are named after their "radiant," e.g., the "Leonids"
- radiant defines the direction from which most of the meteors
originate.
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