A comet is a small astral body, similar in construction to a planet. Its orbit may at times bring it close to the sun and make it visible to the naked eye, or through relatively low strength telescopes, from Earth. When one can be viewed, it is usually noted as having a tail, made of gasses, which early astronomers often mistook for a shooting star.
Most observable comets in our solar system derive from the Oort Cloud, a hypothesized cloud made up of leavings from the sun. These materials form comets, which orbit the sun because they are affected by its gravitational pull. While passing by individual planets, the comet may be affected by the gravitational forces of the planets, thus causing an elliptical or oval-type orbit.
Usually, people on Earth see these astral bodies when they passes in between Earth and the sun. It is thought that the comet and its tail, sometimes called the coma and tail, reflect the light of the sun, enhancing their visibility. Since comets may orbit the sun in strange patterns, people may only see the passage of one in a lifetime.
In fact, comets are usually classed by the length of time it takes them to orbit the sun. A short period one takes up to about 200 years to make a full trip around the sun. A long period comet may take far more time to complete a trip.
For example, Halley’s Comet can be viewed on earth about every 75 years, which makes it part of the short period class. Its last sighting on Earth was in 1986, and it is expected to be seen again in 2061.
A planet may capture a comet, which can cause significant damage to the astral body. Such a gravitational capture may cause it to break into many small pieces, which can then hit the capturing planet. Comet Shoemaker-Levy 9 was observed as broken in 1993, and astronomers were able to witness it hitting the atmosphere of Jupiter in 1994.
Most often, people looking at the night sky may think that they see “falling stars” that are actually meteors or comets. There are thousands of tiny ones that do not attract much interest. The once in a lifetime comets like Halley’s are often thought of as exciting, since most people will only see them with the naked eye once.