Scientists believe that comets are made up of material left over from when the Sun and
the planets were formed. They think that about 100,000 million comets orbit the
Sun.
Some comets orbit the Sun like planets. Their orbits take them very close to and very far
away from the Sun.

A comet is made of dirty ice, dust, and gas. When a comet gets close to the Sun, part of
the ice starts to melt. The solar winds then push the dust and gas released by the melting
ice away from the comet. This forms the comet's tail. Every time a comet comes close to
the Sun, a part of it melts. Over time, it will completely disappear.

A comet does not give off any light of its own. What seems to be light from the comet is
actually a reflection of our Sun's light. Sunlight bounces off the comet's ice particles in the
same way light is reflected by a mirror.

Think of a comet as a big, dirty, gassy snowball. Comets are formed in the ring of rocks,
dust, and ice that orbits the Sun beyond
Pluto called the Kuiper Belt. Comets form when
rocks, dust, and ice condense – that is, join together. As a comet grows larger, it starts to
be pulled towards and around the Sun. Comets in our Solar System usually take many
years to go around the Sun – from a few dozen years to many thousands of years. This is
because they start to orbit the sun from very far away. They make long, egg-shaped orbits
around the Sun instead of almost circular ones like the planets.

The comets that can be seen in the sky without telescopes are unusual because they are
the biggest and brightest comets of all. You might have the chance to see one once or
twice during your life. Most comets can only be seen with a telescope. The few that can be
seen with human eyes are usually just hazy streaks or faint smudges in the night sky.

When comets are very far away from the Sun, they are covered in a coating of icy, black
rocks and dust. As a comet approaches the
Sun, however, the ice starts to melt. This
creates large amounts of water and gas that break through the coating, freeing some of
the dust and rocks. Sometimes this water, gas, rocks, and dust can be seen from the
Earth as one or two tails streaming away from the comet. Even when only one tail can be
seen, there are two, one made from the lighter gas and water, and the other from the
rocks, dust, and chunks of ice.

Comets themselves are usually between a few kilometres and several hundred
kilometres in size, but their tails can be several million kilometres long.

Seeing Comets in the Sky
The "great comets" that produce particularly spectacular tails are some of the rarest
objects in our solar system. Usually they can only be seen about once every hundred
years, so it is very rare to see one of these comets. The last great comet appeared in
1910, but it may still be another hundred years before another one comes near the
Earth.
Astronomers can't predict exactly how or when they will appear as there are still things
about our Solar System that they don't understand. If you hear about a comet coming into
the sky soon, follow the instructions below to watch it!

  • Find out if the comet is going to be in your area of the sky.
  • Tell your parents about the comet's arrival.
  • Get a telescope or binoculars and some chairs to view it. Many of the largest
    comets have never even needed a telescope to see them.
  • Ask your parents to take you to a park, the woods or another dark place away from
    city lights.
  • Look up into the sky and enjoy this amazing sight.
  • Usually the dust making up the comet's tail is so faint you can't see it. However,
    when the Earth's orbit takes it through one of these tails, the dust hits the Earth's
    atmosphere and burns up. These are the recurring meteor showers that happen
    from time to time, and most major meteor showers have now been identified either
    with an existing comet or the remains of a comet that was observed earlier, usually
    in previous centuries. When the Earth travels through this "swarm" of dust left
    behind, you can see shooting stars or meteors at night.

How many Comets are there?
No one really knows. All comets spend most of their orbit so far away from the sun that
they can't be seen -- even with a telescope. However, every year amateur astronomers
discover over 100 never-seen-before comets that have come close enough to be
discovered. As of November 2005, astronomers have discovered 2 857 comets. Most of
the comets we see either crash into the Sun, or leave the Solar System entirely. There
might be millions of these comets that sooner or later will come within range of our
telescopes.

Of all the comets that have ever been seen, astronomers only expect 253 comets to ever
return.

A comet is usually named after the astronomer who first discovered it. When several
people are involved in its discovery, sometimes you will see multiple names on a comet,
like Comet Hale-Bopp, or Comet Shoemaker-Levy. It is generally considered to be a great
honour to have a comet named after you.

In ancient times people didn't have a very good understanding of what comets really were
or where they came from. They were seen as very unusual objects in the sky, and very
temporary in nature as well. In some societies it was often a sign of bad events in the
future when a comet arrived, associated with the death of a king or a significant military
defeat. In other countries comets were considered to bring good luck, bringing increased
fertility and more food. The ancient Chinese astronomers seem to have done the best job
of actually recording when comets appeared in the sky, and left detailed descriptions of
what they looked like and approximately where in the sky each comet was seen.

Even as recently as the 1910 appearance of Halley's Comet there was widespread panic
when it was discovered that the Earth might pass through the tail of that comet. The panic
was over the possibility of gases from the comet flooding the atmosphere of the Earth with
poison. The reality was that there is so little gas in a comet tail that there is no
measurable effect in the content of the Earth's atmosphere when an event like this occurs.

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Our Solar System
Comets
Sites for Teachers
Our Solar System
This comprehensive book
contains information on all
major planets, major star
constellations, space
exploration and our solar
system. Included are fact
sheets, fast facts,
wordsearches, crossword
puzzles, Q's & A's, Student
Activity Sheets,
Teacher/parent resources
and tips, lesson plans and
crafts and activities.  
Preview
entire book 208 pages
The Chinese lunar calendar
dates back to the second
millennium BC. The Chinese
calendar is cyclical. Each
cycle is made up of 12 years;
after the 12th year, the cycle
is repeated.  
This book
contains comprehensive
teacher/parent resources,
lesson plans and activities
relating both to the Chinese
Zodiac and to the Chinese
New Year. A Fun interactive
learning experience for Gr
K-5  with a particular focus
on adjectives,  
characteristics and traits.  
Preview the entire book here