How do comets become visible from time to
Each comet nucleus is moving randomly
within the Oort cloud or the Kuiper belt. Once in a while one of them is disturbed out of
its position by the close passage of another object. As a result, one of the following
three things can happen.
The comet nucleus is pushed away from the solar system
and leaves it altogether.
The comet nucleus is nudged inwards and races towards the
sun, circles it and goes back to return after hundreds or thousands of years. The comet
Hyakutake which delighted millions of people around the world in March 1996 was one such
Orbit change of a comet
due to Jupiter's
The comet nucleus is deflected by a large planet like
Jupiter as it races towards the sun. With its path so altered, it goes round and round the
sun with a period shorter that 200 years. Astronomers call such comets short period
comets. The famous comet Halley is a short period comet deflected by the planet Jupiter
and has a period of about 76 years. Sometimes these comets can also be captured by
Jupiter. This is what happened to the comet Shoemaker - Levy 9, perhaps a hundred years
before it crashed into Jupiter in July 1994.
It is when ( b) or ( c) happens that comets become visible.
The orbits of over 700 comets are known. About a 100 of them have periods shorter than 200
Return to the An Illustrated Guide To Comets page