Comets

Comets are amongst the oldest objects in our solar system, remaining almost unchanged since they were formed billions of years ago. The early solar system was a large flatted disc of cloud that spun slowly, with its centre eventually becoming our Sun. Travelling through this cloud were the comets. As the outskirts of this disc condensed to become the planets, and as they grew, their gravity slung the wandering comets into a large sphere, called the Oort Cloud, which is located beyond Plutos' orbit.

A comet is a snowball several miles wide, packed with rocky or muddy material. In this snowball are ices of water, cyanogens and other materials, including organic materials like Carbon, Hydrogen, Oxygen and Nitrogen (CHON particles). When the object comes near to the Sun, the ice begins to sublimate, releasing gas and dust. This material forms a large head around the nucleus and then streams behind this “Coma” to produce the tail.

The Coma of a comet can be thousands of miles across, with its tail tens of millions of miles long of which there are two main types. An Ion tail, where ionised gas forms a bluish coloured tail, and a dust trail, which generates a yellowish tail comprised of dust particles.

Comets that travel in an elliptical orbit around the sun within a 200 year period are known as short-period comets, the most famous being “Halleys Comet”, which returns every 76 years.

Longer period comets can take thousands of years to return, for example comet “Hale-Bopp” rounded the Sun on its fist visit in over 4000 years during 1997.

Believe it or not, about 25 comets are discovered every year, almost always by amateur astronomers. Many of these discoveries are too faint and small to be seen with the naked eye. However, during the end of 2006 and early 2007 members of the Deise Astronomy Society, witnessed and even imaged the two notable comets crossing our skies at that time.