Transcript Comets
Comets Comets Hale-Bopp and the Andromeda galaxy Comet miscellaneous Discovered as faint, fuzzy patches Travel in highly elliptical orbits Brightens and develops a tail as it nears the Sun Emit no visible light of their own A few dozen are discovered each year, more go by unnoticed Comet miscellaneous They are essentially ice left over from the formation of the gas giants Are named after their discoverers – the first 2 people to report it About half of all discoveries are by amateur astronomers The name comet comes from the Greek word kometes, meaning “wearing long hair” This comet appeared to pass in front of the Ring Nebula An earlier view Parts of a Comet Nucleus: main solid body – Typically only a few kilometers wide – The only part that remains when the comet is far away from the sun Coma: the halo around the nucleus – Forms and becomes larger as the comet comes toward the sun – Can become almost as large as Jupiter or Saturn Parts of a Comet Hydrogen envelope: Surrounds the comet – Invisible, stretches millions of km in space Ion tail: straight, makes glowing linear streamers Dust tail: broad and gently curved – Rich in dust that reflects sunlight Comets tails, cont. Always point away from the sun, due to solar wind Lies outside the comets orbit Is in front of the comet, once it goes around the sun This picture of Hale-Bopp shows the white dust tail and the blue ion tail Dust and ion tails of Comet NEAT Physical Properties Its mass decreases with time (it loses material as it goes around the sun) Made of dust particles, methane, ammonia, carbon monoxide, and water ice Long Period Comets Comets may go as far as 50,000 A.U. from the sun With very elliptical orbits, they slow down, according to Kepler’s 2nd law Most take hundreds of thousands (maybe millions) of years to complete an orbit. May be part of a huge cloud (Oort Cloud) orbiting far from the sun How many comets do you see? Comet Bradford is to the left and Comet LINEAR to the right. Short Period Comets Fewer in number Have orbital periods of less than 200 years Do not venture far beyond the orbit of Pluto Originate in the Kuiper belt Short v’s Long Period Comets Short period comets orbit in roughly the same plane as the planets (ecliptic) Long period comets orbit in all directions Comet Encke returns every 3.3 years. Its orbit goes just outside of Mars and back! Halley’s Comet British astronomer Edmund Halley realized that a comet seen in 1682 was not a one time event. He calculated its path and found that it had an orbital period of 76 years He predicted that it would reappear in 1758 He did not live to see it, but he was correct Halley’s Comet Ancient cultures record Halley’s comet in every pass since 240 B.C. Was photographed in 1910 and again in 1986 In 1986, a Soviet craft, Vega 2, traveled through its coma and was only 8000 km away from its nucleus Halley’s Comet A European spacecraft, Giotto, came within 600 km of its nucleus to take pictures Found that the nucleus was potato shaped (15 km x 10 km) and is almost black Will next be near us in 2061 When it passed in 837 AD, it was as bright as the crescent moon Comet Halley’s nucleus Hale-Bopp Biggest comet to visit the solar system in more than 200 years Was visible to the naked eye for more than a year Will return…in 2,380 years…sorry! Comet Hale-Bopp early after its discovery Comet Shoemaker-Levy 9 Discovered in 1993 orbiting Jupiter Jupiter’s gravity ripped it into 21 pieces These pieces crashed into Jupiter a year later Shoemaker-Levy 9 impacting Jupiter Comet IkeyaShang and the Northern Lights! Comet Hyakutake and a cactus Comet McNaught – 2007 Comet Holmes – Fall 2008 2010 – Comet Hartley2 and the Perseus Double Star Cluster