You can now buy the recently released book, Fall of a Thousand Suns: How Near Misses and Comet Impacts affected the Religious Beliefs of our Ancestors. It is available through iBooks and Amazon.
This website only lists information on modern-day comets and meteor showers. The book, however, thoroughly investigates how specific ancient impacts and near misses changed religious beliefs around the world.
What is the Oort Cloud?
Definition of Oort Cloud
This sphere of billions of comets was born in the mind of Jan Oort in 1950 and remains the king-of-the-hill, accepted theory among astronomers over a half-century later.
Exploded view of thousands of objects in the Kuiper Belt surrounded by hundreds of billions of comet nuclei in the Oort Cloud.
Credit: Don Yeomans/NASA/JPL illustration adapted by Kevin Curran
The Oort Cloud is a hypothetical sphere of comets that stretches from 1,000 to 100,000 AU. In order to give you some idea of how big that is, Voyager 1 (a spacecraft launched by the United States in 1977), is now 11,000,000,000 (118 AU) miles from our Sun. It’s the furthest man-made object from Earth. Despite traveling traveling 38,000 miles (61,000 km) per hour, Voyager 1 won’t reach the near edge of our Oort cloud for another 246 years. It won’t reach the far edge, and exit our solar system, for another 28,000 years. The far edge is the Oort Cloud is roughly 1/4 of the distance to the nearest star.
In the mind of Jan Oort, the Oort Cloud is the breeding ground for long-period comets, some with orbital periods of thousands or even millions of years. Comets from our Oort Cloud are occasionally pushed into the inner solar system by passing stars.
Although often considered a comet from the Oort Cloud, Comet Hale-Bopp (C/1995 O1) has an orbit that only takes it 360 AU from our Sun. So Hale-Bopp actually spends most of its life in the scattered disk beyond the Kuiper Belt rather than the Oort Cloud. It was visible to the naked eye beginning in May of 1996 and remained so for eighteen spectacular months, twice as long as the previous record holder, the Great Comet of 1811.