Comets became popular with the apparition of Halley's in 1986. Sadly, Halley's was a bust, and interest centered around the pronunciation of Edmund's name. After decades of calling him Hey-le, he suddenly became Hal-le. Comets are unpredictable, and Halley's has not been the only dud! Both Kohoutek and ISON fizzled. There is always hype surrounding comets. ISON was predicted to be as bright as a full moon! Being a sungrazer, it failed to survive perihelion.
It was the unpredictability that caused fear in ancient people. The sun, moon, planets & stars had regular patterns. Comets appeared seemingly for no reason and were considered bad omens.
Comets are stuff left over from the formation of the solar system. Stuff was blown out when the sun turned on. There are trillions of comets in the Oort Cloud at the edge of the solar system, that region named after Dutch astronomer Jan Oort. Of 4000 known comets, I have seen 3.
Comets orbit the sun like planets, but their orbits are extremely elliptical. As comets approach the sun, ethane and methane vaporize to form tails millions of miles long.
Comets have 2 parts: heads about 6 miles wide and fan-shaped tails. Blue gas tails shine when excited by the solar wind. Dust tails reflect sunlight.
Comets approach the sun head first. When leaving the sun, it is the other way around. Tails take the lead. Either way, tails point away from the sun, driven out by the solar wind.
Comets cause meteor showers. As comets circle the sun, debris is strung out along their orbits. When our planet crosses these streams, meteoroids as small as apple seeds enter the atmosphere. They flare up because of friction.
1 The Great Comet of 1744
This one had 6 tails.
2 The Great Comet of 1861
This comet looked huge because it came within 12 million miles of Earth. It was a fearsome spectacle!
3 Halley's Comet 1910
Halley's Comet was recorded as far back as 467 B.C. Edmund Halley's research led him to predict it was returning every 76 years. When it returned in 1758, it made him famous. Halley's is a short-period comet. Long-period comets take thousands of years to return. Halley's was spectacular in 1910, and the earth passed through the tail.
4 Comet Ikeya-Seki 1965
I saw this comet on Halloween morning. Ikeya-Seki was a sun-grazer and split in 2 after emerging from behind the sun. Its tail was 90 million miles long, one of the longest.
5 Comet Bennett 1970
Passing near the Cygnus star cloud, this comet had a tail 10 degrees long. John Bennett discovered it. I was in the army and out of astronomy.
6 Comet West 1976
Comet West was as bright as Jupiter and had a tail 20 degrees long. Richard West discovered it. I was at Peabody College in Nashville and unaware of it.
7 Shoemaker-Levy 9 1994
The Hubble Space Telescope imaged this as it crashed into Jupiter. 21 fragments hit! It was discovered orbiting Jupiter, captured by the planet's gravity. Gene Shoemaker died in a car wreck in Australia.
8 Hyakutake 1996
I saw Hyakutake! Its head was zero magnitude. The blue gas tail was 12 million miles long. Dust tails are brighter than gas tails.
9 Hale-Bopp 1997
Discovered by Alan Hale and Thomas Bopp, it became the darling of comet buffs. It was brighter than zero magnitude and visible in amateur telescopes for 2 years. Hale-Bopp showed 2 distinct tails. The blue gas tail and dust tail were widely separated. Hale-Bopp was bright because of its size. Its head was 25 miles in diameter. I saw it from my parents' yard on Aiken Road. Comets are brighter when near the sun because more ice has vaporized.
Astronomers make a big deal out of comets. Theorists have gone so far as suggesting that comets brought water to Earth, that they are responsible for the oceans. Moreover, they maintain that comets may have provided the organic molecules that started life. It sounds crazy, but more and more theories are cosmic rather than Earth-based. It seems that trillions of trillions of trillions of comets would have had to impact Earth to create the oceans.