Comets are scraps left over from the formation of the solar system. There was a lot of debris, and craterization took place on a massive scale. Comets orbit the sun. They develop tails as the sun melts ammonia and methane. Tails are millions of miles long and point away from the sun, driven out by the solar wind. Halley's comet orbits beyond Neptune, returning every 75 years. Halley was not the first to see his comet but the first to predict its return.
I saw comet Comet Ikeya-Seki on Halloween morning, 1965. It was fuzzy and dim but worthwhile. I saw Hyakutake in 1996 and Hale-Bopp in 1997.
It took 30 years to see my second comet, which I spotted the morning of March 24, 1996. Hyakutake was as bright as the Big Dipper stars and extended its handle. It was fuzzy with no discernible tail. Two mornings later, it was close to the Little Dipper. The morning of March 27, it was below the North Star. Hyakutake upstaged the highly-pulicized Hale-Bopp.
Shoemaker-Levy 9's impact with Jupiter gave astronomers their first glimpse of a collision in space. Jupiter is a vacuum cleaner, sucking up stuff and protecting Earth.
I began watching the Perseids in the early 1960s. The Perseids occur in August. It is the best meteor shower. The night of August 11 and morning of August 12, 1964, I counted 351 meteors. Toward morning they were dropping in the east like snowflakes. Many were bolides, leaving bright trails. The best one appeared after daybreak. Cousin Larry was yelling, and I looked up to see a meteor the size of a half moon. It was exploding and changing colors.
Meteor showers are associated with comets, and the Perseids are associated with Swift-Tuttle. As Swift-Tuttle orbits the sun, it leaves behind debris. Meteoroids string out along its path. Most of the meteors entering the atmosphere are like grains of sand. They are vaporized by friction a hundred miles up. In a shower meteors emanate from a point called the radiant. Showers are named for the constellations behind their radiants. We see more meteors toward morning because the earth meets them head on.
Meteorites are objects that survive and fall to earth. They are made of iron and nickel. Meteor Crater near Winslow, Arizona, is evidence of a large meteorite which impacted Earth 50,000 years ago.
200 impact craters have been found around the world. One is near Odessa, Texas. O. Richard Norton says meteorites are pieces of asteroids. The largest found in the United States came from Willamette, Oregon. I saw it in the American Museum of Natural History in New York.
There is one case of a person being hit by a meteorite. In 1954 a woman in Alabama was sleeping on her couch when a meteorite crashed through the roof. It ricocheted and hit her in the side.
Comets and asteroids leave craters. The idea that the dinosaurs were killed by an asteroid has been accepted. Scientists point to the Chicxulub (Cheek-shoe-lube) crater in Mexico's Yucatan peninsula as the impact that killed the dinosaurs and two-thirds of all species. Evolution may be driven by impacts.
Something hit Siberia in 1908. It is called the Tunguska Event. Trees were flattened, but no crater was found. The comet or asteroid vaporized before impact.
Earth's atmosphere acts like sandpaper, smoothing craters out. Water erodes, and plate tectonics reshape the earth. Otherwise, the earth would look like the moon.
