(IAAC) Comets : the @stro object for the week of 04/03/2000

@stro object of the week
drafted by the @stro pages
the week of 04/03/2000
highlighted this week: Comets
Comets are large conglomerations of ice, dust and rock believed to be relics
left over from the formation of the solar system and are often compared to
"dirty snowballs". Comets are thought to reside in the outer regions of the
solar system known as the "Kuiper Belt" and the "Oort Cloud". Their distant
orbit around the Sun is sometimes perturbed by the gravity of passing stars
or the large gas planets and a comet can subsequently be thrown into our
area of the solar system where they are occasionally visible to the naked
In the outer regions of the solar system comets are dormant and appear much
like asteroids. When a comet gets closer to the inner solar system it can
come to life and develop an active tail. This tail consists of gas, dust,
ice and rock which is sloughed off and pushed away from the comet by the
solar wind and heat produced by the Sun. An interesting note is that the
tail always points away from the Sun regardless of what direction it is
traveling in relation to the Sun.
Comet compositions and descriptions can vary from comet to comet. Some of
the chemicals found in comets include methane, ethane, carbon monoxide, and
they are also sources of large amounts of water. Comets are thought to have
an average diameter of around 3 miles (5 kilometers), but some comets exceed
this amount, such as Hale-Bopp which was about 25 mi. (40 km) wide.
There are several current theories that relate to comets. Those with large
implications to science include the theories that comets brought water to
Earth's surface and could have delivered chemicals essential to life on
Earth. Other theories even suggest that comets transport microscopic
bacterial life, although no direct evidence for this is currently available.
It was believed for eons that comets influenced human existence as
harbingers of doom or predictors of other major events yet to come. In
present times comets are not thought to directly affect life on Earth with
the possible exception of a cometary impact on Earth, or the observation of
various meteor showers left behind by comet tails. However, they are
followed intensely for many reasons including their close relationship to
the formation of the solar system.
Comets are one of the few astronomical bodies that a person can name for
themselves - the discoverer of a new comet gets to name it, so comets are
usually named after the person that found them.
Some famous naked-eye comets include:
Comet Hale-Bopp (discovered in 1995)
Comet Hyakutake (discovered in 1996)
Comet Shoemaker-Levy 9 (discovered in 1993)
Comet West (1975)
Comet Halley (first named in 1682)
more information about comets...
more information about comets from the U. of Michigan...
more about the Kuiper Belt and Oort Cloud...
make a "kitchen comet"...
more on Comet Hale-Bopp...
the image that accompanies this article...
Clear skies,
Roger Herzler
the @stro pages
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