Comets

A comet an orbiting mass of ice and snow, surrounded by gas. Because the
solid part of the comet is small, less than 4 miles in diameter, it does not
have enough gravity to pull all its mass down to sphere. For that reason,
the head of the comet is quit irregular in shape, not spherical like a planet
. Actually, the "head" of the comet refers to the solid part and the cloud of
gas that surrounds it. People often think of comets as glowing, hot objects.
This could not be farther from the truth. Comets are very, very cold.
The light that we see when we observe them is partly sunlight reflected or
scattered by gas and debris. I'll talk about the comet's own light later.

When the comet is very far from the sun, there is only a little gas around it.
The orbit of the comet is very elongated. That is, it passes very close to the
sun, then travels very far away, turns around and comes back around.
When the comet is fairly close to the the sun ( 2 or 3 times as far away
from it as the Earth is ) the suns rays begin to warm its surface. Molecules
boil off the surface along with dust particles. The closer it gets to the sun,
the more energy falls on its surface. When it is about as far from the sun as
the Earth, it gets about the same warming effect as the Earth. More and
more water and some hydrogen are released as it gets closer to the sun.

The gases around the core of the comet glow when they are struck by
ultraviolet rays from the sun. The gases literally glow. So, at this stage
the comet adds its own light to the reflected sunlight. The flow
( fluorescence ) of the gases becomes even more intense than the sunlight.

The radiation and particles that stream out from the sun, sweep past and
through the gas/dust envelope around the comet. With an effect much like
the wind blowing leaves, the gas and the dust are "blown" away from the comet's head. They stream out, away from it, in the direction opposite
the sun. This makes the comet's long tail. The tail is always pointed away from the sun. It's
direction has nothing to do with the direction the comet is moving. When
the comet is moving away from the sun, the tail is ahead of it,
not behind it !

All rights reserved. Stephen Tuell 2007

 Photo of Hale-Bopp on Feb. 6th, 1996 ( Visit this page )

Press information Sheet on Comet Hale-Bopp ( Visit this page )

Links to Other Comet Hale-Bopp Home Pages ( Visit this page )

Comet Hale-Bopp for the Non-Astronomer ( Visit this page )

Comet Hale-Bopp ( a page from Japan ) ( Visit this page )

Palomar Image of Comet Hale-Bopp ( Visit this page )

Comet Hyakutake

On the Tail of A Comet: The Hyakutake Compendium ( Visit this page )

Comet Hyakutake Pages ( Visit this page )

Observations of Comet Hyakutake ( Visit this page )

Comet C/1996 B2 Hyakutake ( Visit this page )

Comet Shoemaker-Levy

Comet Shoemaker-Levy Collision with Jupiter ( Visit this page )

JUPITER'S BRUISES Shoemaker-Levy 9 has met its doom,
but the postmortem has just begun ( Visit this page )

General information about comets

Comet Definitions ( Visit this page )

Gary Kronk's Comet Page ( Visit this page )

SKY Online's Comet Page ( Visit this page )

WHAT IF A COMET HITS EARTH? ( Visit this page )

Comets and the Bronze Age Collapse ( Visit this page )

A Tale of Two Comets ( Visit this page )

The Ulysses Comet Watch ( Visit this page )

Comet Light Curves ( Visit this page )