The first Space Exploration started in 1957 with the launch of the first artificial satellite, Sputnik 1, sent into space by the Soviets. Since ancient times people have dreamed of leaving their home planet and exploring other worlds not known to man. Every era through out history has had a belief as to what the "heavens" are made form. The Greeks believed that the stars and space were made of a material called "Quitenses", and other culture once thought that the stars were made of their peoples passed away.
We know now what stars are really made of; they are made of various gases that explode over and over again. Up until about 43 years ago people did not have the means to travel to or send objects into space. The hardest part of traveling into space was developing rockets that were powerful enough and reliable enough to boost an object into space.
Common heard of Space Exploration terms are Comets and Asteroid's. A comet is basically small, rocky, and icy and revolves around the sun. When a comet passes close to the sun some of the ice turns to gas. This gas and some loose dust creates a long, bright tail that trails behind the comet.
If a comet was to hit the earth, it would cause some serious damage. As an example even if something relatively small in size hit the earth, it would cause great damage. Small from an comet's point of size is around 200 metres in diameter and if this was to hit an ocean it would create devastation to all cities within a large radius.
Asteroid's are described as small or minor planets that are members of the solar system and move in what are called elliptical orbits. They are usually found between the orbits of Mars and Jupiter.