What are comets?
Have you ever looked up and saw a comet zoom in and out of view? Did you
wonder what it was made of, or why it glowed?
Most comets are very dim and can only be seen with a telescope because comets
don’t give off light of their own. The light from the Sun shines on them and
makes them look like they are glowing. The closer a comet gets to the Sun, the
brighter it glows.
A comet is like a large, icy rock that travels in an orbit (path) around the
Sun. A comet’s orbit is very long and elliptical (like a circle squished into
an oval).
Most comets have a rocky center called a nucleus. Around the nucleus are bits
of dust and pebbles held together by ice and frozen gases. When a comet gets
closer to the Sun, the ice and frozen gases start to melt. This creates a hazy
cloud around the nucleus. The hazy cloud is called a coma. The nucleus and coma
make the head of the comet.
As the comet gets closer and closer to the Sun, the coma starts to grow
larger and stretch out behind the comet. As the coma stretches, a tail is
formed. The closer the comet gets to the Sun, the longer the tail gets.
How is the tail created?
A comet gets a tail as it gets closer to the Sun because atomic particles are
streaming out from the Sun. Atomic particles are so small that you can’t even
see them with a regular microscope! These atomic particles create a solar wind.
When the comet is about 150 million miles from the Sun (a little farther from
the Sun than Mars), the solar wind is strong enough to push some of the melted
ice and gases away from the comet. This melted ice and gas create the comet’s
tail.
A comet can have different types of tails that can stretch over millions of
miles. The different types are:
- Straight tail (extends straight behind the comet’s nucleus)
- Curved tail (curves along the comet’s orbit)
- Multiple tails (there appears to be more than one tail)
The tail is spread so thin that there is barely anything there! If you could
fill a bucket with comet tail and compare it to a bucket filled with air, then
the bucket filled with air would have billions of more matter than the one
filled with comet tail.
As the comet moves away from the Sun, its tail starts to shrink, and its
nucleus starts to freeze again.
Every time a comet goes around the Sun it loses a little bit of gas, ice, and
dust. These pieces spread over the orbit of the comet until the entire orbit has
bits of dust, gas, and ice over it. Soon all that is left of the comet is the
rocky center. Comets that do not have a rocky center completely break up over
time.
