What Is A Comet?
What is the speculated cause of the distinction of dinosaurs?
Comets are often referred to as ‘dirty snowballs'. They are what is left over after the formation of the stars and planets billions of years ago.They live in an area of space outside the orbit of Pluto called the Oort cloud, named after the Dutch Astronomer Jan Oort who first proposed its existence in 1950.The Oort cloud is an immense spherical cloud surrounding our solar system; its vast distance is considered to be the furthest edge of the Sun's gravitational effect.Comets are usually made of chunks of frozen gases, rock and Ice. They are not very big compared to a planet or Moon, the largest being perhaps a few hundred kilometres across but most being less than a kilometre. Millions of Comets usually live peacefully in this Oort cloud, orbiting around the Sun, billions of miles deep into Space. But every now and again one of them may get disturbed in its orbit and begin to fall in towards the Sun, and this is where the fun begins!As it passes the outer planets on its journey towards the Sun it begins to warm up, and as it warms up it starts to evaporate and the internal gases start to escape.The closer it gets to the Sun the more extreme the warming becomes and the more violent the gas escapes until the comet begins to form a tail of gas and debris streaming from it. It is now that it becomes visible as what we know of as a comet.A really large comet can produce a spectacular tail and will be seen clearly from Earth for many weeks moving against the background stars on its journey towards the Sun.Ancient civilisations sometimes believed they were omens of doom and it was not until 1682 that the English astronomer Edmund Halley realized that the comet he was observing was the same one that had been seen every 76 years since 1066, he predicted its return in 1758 and it became known as Halley's Comet. Halley's Comet was depicted in the Bayeux tapestry during the Battle of Hastings.During Halley's Comet last return in 1986 it was met by no less than 4 probes sent from various nations on Earth and for the first time we were able to see close up images of what a comet actually looks like. Comets are usually named after the person who first discovers them. In 1997 a truly magnificent comet was discovered by Alan Hale and Thomas Bopp and was seen by most of the northern hemisphere for many weeks and called comet Hale-Bopp.Sometimes the Comet is on a direct collision with the Sun and gets sucked into it, others swing past the Sun and they are thrown into a very elliptical orbit bringing them back again as in the case of Halley's Comet whilst others are thrown back out into deep space, never to be seen again.But because the tail of the comet is produced by radiation from the Sun, it always points away from the Sun no matter which way the comet is travelling. As the comet moves away from the Sun it will travel tail first. Occasionally some comets don't make it in to the Sun but collide with objects in the solar system. One such case was in 1994 when comet Shoemaker-Levy 9 broke up into over twenty pieces and collided with the planet Jupiter.It is now thought that a comet crashed into the Earth 60 million years ago and caused the extinction of the dinosaurs. Astronomers believe it is only a matter of time before we are hit by another one, let's just hope it's not soon.