Halley's Comet

PRONOUNCIATION KEY:Halley is often pronounced haeli

Definition: Halley's Comet  is a comet that can be seen every 75–76 years this is the most famous of all periodic comets.Halley is the only short-period comet that is clearly visible to the naked eye, and thus, the only naked-eye comet certain to return within a human lifetime.

   Halley's Comet last appeared in the inner Solar System in 1986, and will next appear in mid 2061.

   Comets are believed to have two separate points of origin in the Solar System: the Kuiper belt, a flat disc of icy debris between 38 AU* (Pluto's orbit) and 50 AU from the Sun, and the Oort cloud, a sphere of cometary bodies which has its inner edge at 50,000 AU. Short period comets (those with orbits lasting 200 years or less) are generally accepted to have emerged from the Kuiper belt, while long period comets, such as Hale-Bopp, whose orbits last for thousands of years, are believed to originate in the Oort cloud. Halley is unusual in that while it is a short period comet, its ultimate origin lies in the Oort cloud, not the Kuiper belt.

    Halley's comet is named after Edmond G. Halley who was the first to suggest that comets were natural phenomena of the solar system, in orbit around the Sun.He suggested that a certain comet was a regular visitor, returning every 76 years, and was, in fact, the same one which had been observed since 240 BC. In 1682 he predicted the comet would return again in 1758, and sure enough, the comet arrived in March 1759. Halley's comet made a particularly bright appearance in 1910. It also was recorded in a famous ancient tapestry after its 1066 appearance.

AU:the distaince from the sun to the earth

The reason we need learn about halley's comet is it will give us a better understanding of comets because halley,s comet is a periodic comet we can study it and bredict what other comets look like and what they may do when they come close to the sun and ower planet.

 1."Halley's Comet." Wikipedia. 9 May 2008 <http://en.wikipedia.org/wiki/Halley's_Comet>.

 2."Halley's comet." 06/december/2000. 15 May 2008 <http://www.windows.ucar.edu/tour/link=/comets/Halleys_comet.html>.