Comet - 1
Comets -1
Comets are small, fragile, irregularly shaped bodies
composed of a mixture of non-volatile grains and frozen gases.
They have highly elliptical orbits that bring them very close
to the Sun and swing them deeply into space, often beyond the
orbit of Pluto.
As comets approach the Sun they develop enormous tails of
luminous material that extend for millions of kilometers from
the head, away from the Sun. When far from the Sun, the nucleus
is very cold and its material is frozen solid within the nucleus.
In this state comets are sometimes referred to as a "dirty iceberg"
or "dirty snowball," since over half of their material is ice.
When a comet approaches within a few AU
of the Sun, the surface of the
nucleus begins to warm, and volatiles evaporate. The evaporated
molecules boil off and carry small solid particles with them,
forming the comet's coma of gas and dust.
Physical Characteristics :
The solid nucleus or core of a comet consists mostly of ice and dust coated with dark organic material, with the ice composed mainly of frozen water
but perhaps other frozen substances as well, such as ammonia, carbon
dioxide, carbon monoxide and methane. The nucleus might have a small
rocky core.As a comet gets closer to the sun, the ice on the surface of the nucleus begins turning into gas, forming a cloud known as the coma. Radiation from the sun pushes dust particles away from the coma, forming a dust tail, while charged particles from the sun convert some of the comet's gases into ions, forming an ion tail. Since comet tails are shaped by sunlight and the solar wind, they always point away from the sun.
The nuclei of most comets are thought to measure 10 miles (16 km) or less. Some comets have comas that can reach nearly 1 million miles (1.6 million kilometers) wide, and some have tails reaching 100 million miles (160 million kilometers) long.
We can see a number of comets with the naked eye when they pass close to the sun because their comas and tails reflect sunlight or even glow because of energy they absorb from the sun. However, most comets are too small or too faint to be seen without a telescope.
Comets leave a trail of debris behind them that can lead to meteor showers on Earth. For instance, the Perseid meteor shower occurs every year between August 9 and 13 when the Earth passes through the orbit of the Swift-Tuttle comet.
Naming :
In general, comets are named after their discoverer, either a person. For example, comet Shoemaker-Levy 9 got its name because it was the ninth short-periodic comet discovered by Eugene and Carolyn Shoemaker and David Levy. Spacecraft have proven very effective at spotting comets as well, so the names of many comets incorporate the names of missions such as SOHO or WISE.
(Hally's comet)
COMET
HALE-BOPP)
(comet hyakutake)
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