|Swamy, K.S. Krishna. Physics of Comets. World Scientific Publishing Company, 1986.||"The total number of comets catalogued at the present time is around 630."||630|
|Comet. Encyclopaedia Britannica. Encyclopaedia Britannica Online. 2009.||"The Catalog of Cometary Orbits compiled by Marsden remains the standard for orbital statistics. Its 1989 edition lists 1,292 computed orbits."||1,292|
|Short, Nicolas M. Comets and Asteroids. Remote Sensing Tutorial. NASA. 20 June 2002.||"The number of comets - most still undetected - within the solar system may be in the trillions."||trillions|
|Vsekhsivatskii, S.K. Comets, Small Bodies, and Problems of the Solar System. Publications of the Astronomical Society of the Pacific, Vol. 74, No. 437 (1962) 106.||"The calculation of the number comets in the solar system gives values of 1011 to 1012.||1011 to 1012|
|MPC Archive Statistics. Minor Planet Center. 9 May 2009.||"The listing below shows the increase in the size of the observational archive. A grand total (including both comets and minor planets) is given at the completion of each batch of Minor Planet Circulars, as well as individual totals for each class of object. Each class of object is further subdivided: minor planets are divided into numbered and unnumbered objects; comets are divided into numbered periodic and other comets (the other comets also includes the unnumbered periodic comets)."
Every five to ten years, a comet can be seen in the sky with our naked eye resulting in a spectacular sight to be remembered. Sometimes these comets will not be seen again in many years and some will never be seen again. A comet is an icy body that orbits the sun in elliptical orbits and it is made up of a mixture of ice, dust, and frozen gases. When seen in the sky, comets are known for their two distinct properties: the coma and the tail. As a comet is coming into the solar system, the nucleus of the comet, which is made up of ice, melts due to the heat from the sun and releases gas and dust particles which forms the comet's coma. The tail, on the other hand, is formed when radiation from the sun and solar wind push against the coma. Comas can reach up to 1 million miles in length and some tails can reach up to 100 million miles in length.
Comets originate in two regions, the Kuiper Belt and the Oort Cloud. Comets from the Kuiper Belt are short-period comets because they orbit the sun in a short time. Comets from the Oort Cloud are long-period comets because of the long time they take to orbit the sun. These regions are estimated to contain trillions of comets with values from 1011 to 1012 comets. By 1986, 630 comets have been catalogued by scientists. There are trillions of comets that exist in the solar system, but as of 2009, only 465,453 comets have been detected by scientists through the use of telescope, satellites, etc.
Jeffrey Yep -- 2009