Recently a meteor streaked across the sky over Toronto giving many folks an amazing light show. It also happened to fortuitously coincide with St. Patrick's Day and The Science Channel's airing of an old episode of "The Cosmic Odyssey" which featured asteroids and comets. They're fascinating, awe-inspiring visitors from the outer reaches of our little corner of the universe. There seems to be two main sources of asteroids and comets: the Kuiper Belt which is fairly close by, and the Oort Cloud which is much farther away. The way I understand it comets and asteroids from the Kuiper Belt visit the Earth in a matter of hundreds of years while objects from the Oort Cloud don't come around but every 10,000 years or more. It was good 'ol Ed Halley who first hypothesized that comets might return within a measurable and predictable time frame. Thanks to the recordkeeping of the Chinese, history proved him right. Thus, he got a comet named after him. Not only are these visitors interesting, they're pretty scary.
Asteroids are comparatively slower movers with a straight shot, therefore we know of their movements well in advance of their approach to our solar system. Not so comets. Since they come at us from all angles they can surprise us with little or no warning. Back when our solar system was still young the Earth was bombarded by countless chunks of these space rocks. If we could have seen the primordial sky it would have been filled with many huge fireballs. Today, most of what makes it to our planet falls in the form of fine dust with meteorites only reaching the ground every once in a while. Apparently, large destructive asteroids or comets only impact our planet every 100 years or so. Since the last major impact took place in 1909, in Tunguska, Russia it seems we could be due for another soon. But thanks to the enormous gravity of the gas giants, especially Saturn and Jupiter, most of these visitors miss us. We didn't used to be sure about whether or not comets could cause damage but in 1994, we got lucky and witnessed the impact of comet Shoemaker-Levy 9 as its remaining chunks slammed into Jupiter.
Not only was it a helluva show but the scientific community learned a lot about comets and impacts, not least of which being the fact that major impacts can and still do happen. The scientific world of asteroids and comets is fascinating, filled with all kinds of way out there facts. For instance, many scientists now believe that most of the water on our little world may have come to us from icy comet impacts, thus allowing life to emerge. There's even a theory that the extinction of the dinosaurs could have been over and done with in as little as 20 minutes.
The lore regarding comets and asteroids is equally rich and fascinating. In ancient cultures shooting stars were often seen as omens or as messages from the gods. After Julius Caesar's assassination, which took place during this time of year, a comet visible over the Mediterranean was considered an indication of his ascension to the heavens, thus making it utterly sensible to deify him, even though he did propel the Empire into civil war. We know that comet better as Hale-Bopp. During the Middle Ages Halley's Comet was reviled in Switzerland as the cause of earthquakes, illnesses, "red rain" and animal mutations and in England for the Black Death. Halley's was so bound up in these horrible events that the Pope at the time felt it necessary to excommunicate the comet! The Incas recorded the appearance of a comet soon before the arrival of Pizarro. A comet was considered a portent of the Norman conquest of England. And one of the most honored Islamic relics is a meteorite from a comet. American Indian legend also has a rich store of comet and meteor lore, including one legend that meteorites are the fecal waste of the stars! Whatever path you walk, I urge you to take time to learn about the magic and wonder and power of these heavenly visitors.