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.
How does a comet get its name?
How does a Comet get its Informal Name?
On July 23, 1995 comet-hunter Alan Hale was in his driveway in New Mexico, while hundreds of miles away Thomas Bopp peered into the eyepiece of his friend’s telescope in Arizona. Both spotted a faint comet between Jupiter and Saturn. It was named Comet Hale-Bopp after its co-discoverers.
Comets are traditionally named after their discoverer, co-discoverers or the automated system that first identified the comet. Historically there have been exceptions to this rule. Halley's Comet (1P/Halley) and Comet Encke (2P/Encke) were both comets named after the individual who first determined their orbit, not the first person to spot the comet in the night sky. Today, comets receive their informal and formal name from the Committee on Small Bodies Nomenclature based on the information they're given at the time of discovery.
How does a Comet get its Formal Name?
Comet Hale-Bopp’s formal name is C/1995 O1. How did it get this name?
Comets are assigned formal names by The International Astronomical Union. They divided each of the twelve months into two parts, and assigned each half-month a letter. The twenty-four letters are A-H and J-Y. The number following the letter indicates its order in the discoveries for that half-month. So, broken down into its parts, C/1995 O1 means it was “1”st “C”omet discovered during the second half of July “O” in “1995.” Once the time it takes to orbit the Sun has been confirmed by multiple returns to the inner solar system, C/1995 O1 will be assigned another name (1P/Halley, 2P/Encke, 280P/Larsen, etc.).
Occasaionlly a formal name begins with "X" or "D", instead of "C". "X" indicates that the original comet has fragmented and is now known by its fragments names. "D" indicates that the comet died, as was the case when Comet Shoemaker-Levy 9 slammed into Jupiter in 1994. Shoemaker-Levy 9 went from being known as C/1993 F2 to D/1993 F2.
The vast majority of comets spend most of their life in the Oort Cloud or Kuiper Belt, which means that they can only be seen with modern-day telescopes once they pass the orbit of Saturn and begin to expel material to form the coma. This creates a problem. What If an astronomer wants to refer specifically to the appearance of Halley's Comet in 1910? They might not say "1P/Halley" in 1910, but instead use another type of formal comet name which refers to the "recovery" of Halley's Comet during that given orbit - 1P/1909 R1. This name refers to the fact that the first comet to have its periodic orbit determined "1P" was spotted for the first time in decades in the first half "1" of October "R" in "1909".
As of March 17, 2013, the orbital periods (“P”) of only 280 comets had been definitively determined.
Ancient Comet Observations
In many cases astrophysicists determine that a discovery is actually a "rediscovery". The initial discovery was simply not observed carefully enough in order to accurately determine when the comet would return to the inner solar system. When a comet's return was not predicted or was inaccurately predicted, the comet was considered "lost". Ambiguities in historical observations occurred prior to 1950, so it's not uncommon to find that a comet was once known by another name.
Historical records of comet observations, including The Book of Silk (168 BCE), date to at least the first millennium BCE. Comets, although unnamed in historical records, have occasionally been retroactively identified as previous orbits of comets known in the modern day.