As a result of their ability to awe and their apparent unpredictibility, great importance used to be attached to comets. They came to be viewed as omens, usually bad ones. In particular, Halley s comet has been associated with the destruction of Jerusalem in A.D. 70 and the Norman Invasion of England in 1066. In mediaeval times it was believed that comets were an atmospheric effect. However, in 1577 the astronomer Tycho Brahe compared observations from different points on Earth and proved that the comet being observed lay well outside the atmosphere.
Astronomers now study comets from a scientific viewpoint.
Although much is now known about them, they remain one of the most mysterious yet beautiful members of the solar system. Most bodies in the solar system move around the Sun in nearly circular orbits in the plane of the solar system. Indeed, some comets that have been seen are on paths that will send them flying out of the solar system for ever. According to one popular theory, they come from a huge spherical cloud of comets that stretches over a thousand times further from the Sun than far-off Pluto. When this happens, some comets could find themselves nudged into new orbits that would take them into the inner parts of the solar system.