are small, irregularly shaped bodies composed of a mixture of
rock, organic molecules and frozen gases. When in the proximity
of the Sun, they are usually characterised by a long tail which
is composed of material vaporised off the comet body. Some
originate from the Edgeworth-Kuiper Belt, beyond Neptune, and
some from the Oort cloud, a spherical shell comprised of
millions of bodies at the edge of our solar system.
The orbit of a Comet usually takes them
to the cold and dark outermost reaches of the solar system to close passesof the Sun. When comets venture into the more intense sunlight of the inner solar system, the ices on the comet nucleus begin to melt and fall away. The wake of particles forms the comet's tail, which can be hundreds of miles long and can often be seen from Earth.
Space Comet are thought to have created major changes to Earth's early atmosphere and
climate by striking Earth billions of years ago. They may have delivered the first carbon-based molecules to our planet.
Halley's Comet is named
after Edmund Halley (1656-1742). Halley was the first person to
predict the return of a comet to the inner solar system in a
regular orbit. Halley's Comet orbits the Sun every 76 years. The
most recent appearance was in 1986. Halley's Comet will be next
visible from Earth in 2061.
Halley's comet orbital
period is on average 76 years, however its orbital path can vary
due to to gravitational fields of the major planets. In the last
2000 years, it has varied by as much as four years.
Other famous Space Comets
are: Comet Neat, Comet Machholz (official designation C/2004 Q2),
Hale-Bopp has an orbital period of 4026 years.
The visit of the
comet in 1997 gave one of the brightest views of a comet since
1811, visible even from brightly lit cities.
Long Period Comets
(Non-periodic comets) are comets that do not have confirmed
observations at more than one perihelion passage and generally
have orbital periods of 200 years or more.
Comet Hale-Bopp -
discovered July 23, 1995
Comet by Carl Sagan,
Ann Druyan (Contributor)
Impact!: The Threat of Comets and Asteroids
by Gerrit L. Verschuur
Shoemaker by Levy by
David H. Levy