What Makes Up Our Solar System? Comets
Space and Astrology 6/21/11
By: Yona Williams
There are a handful of objects and celestial events that the human eye can detect from Earth. For example, every so often, we are treated to an appearance of Haley's Comet Ã¢â‚¬â€œ an infamous short-period comet that appears every 75 to 76 years. In this article, you will learn about the different parts of a comet, as well as other facts and trivia.
What is a Comet?
Known for their very long tails, comets are small, icy bodies that orbit the Sun. A comet is comprised of a nucleus, gaseous coma, and a long tail made out of dust and ionized gases. A comet gets its tail when it comes close to the Sun. Because of the force of the solar wind, the lengthy tail of a comet always points away from the Sun. Sometimes, the tail can reach lengths of up to 250 million km long. When you spot a comet, it is the tail that you mostly see. Catching sight of a comet is only possible when they come close enough to the Sun during their orbit.
Parts of a Comet
Nucleus Ã¢â‚¬â€œ At the head of the comet, there is a frozen center called the nucleus, which is made out of ice, gas, and dust. Although the nucleus is very small (only about 1 to 10 km across), it is where you will find most of the comet's mass.
Coma Ã¢â‚¬â€œ Surrounding the nucleus of the comet, the coma is a roughly spherical blob of gas that measures about 1 million km across. The coma is comprised of water vapor, carbon dioxide gas, ammonia, dust, and neutral gases that were once part of the solid nucleus. It is the coma and the nucleus that create the head of a comet.
Ion Tail Ã¢â‚¬â€œ Solar wind causes a tail of charged gases (called ions) to face away from the sun. This part of the comet can measure more than 100 million km long. When the comet comes close to the Sun, the ion tail trails behind the comet. When the comet is leaving the Sun, the ion tail leads. The tail starts to fade as the comet moves farther from the Sun.
Dust Tail Ã¢â‚¬â€œ Microscopic dust particles make up the long, wide tail known as the 'dust tail,' which slightly curves according to the motion of the comet. As the comet moves away from the Sun, this tail starts to fade.
There is also a Hydrogen Envelope that surrounds the coma of the comet and trails along for millions of miles. This pocket of hydrogen gas is typically found between the ion tail and the dust tail. The hydrogen envelope measures about 10 million km across at the nucleus of the comet, and is around 100 million km long. This part of the comet becomes larger when it comes closer to the Sun.
The Orbit of a Comet
The orbit of a comet around the Sun is often describes as a highly elliptical orbit. As a comet comes closer to the Sun, their velocity greatly increases. When it is farther away from the Sun, the comet slows down. Since the comet becomes lighter when it is near the Sun, they are nearly invisible (or dark) for the rest of their orbit. Some comets actually crash into the Sun, or simply burn up if they get too close to the Sun. This type of comet is called a sungrazer.