Astronomical events are used to help date historical events. (Wikipedia - Astronomical chronology) Which are the most important for this? For example, Josephus recorded a lunar eclipse that occurred prior to Herod the Great's death. Historians attempt to pinpoint which eclipse Josephus mentioned so we can know when Herod died. So my question is, which recorded astronomical events have been the most helpful or most effective in dating historical events?
Our dating system (assuming "ours" refers to the one used in mainstream western culture) is not based on astronomical events at all, It's based on the belief/records/mythology (pick your term according to your personal tastes) of the Christian religion - and even then, the creators of the system apparently got it wrong, as others have computed the date of Christ's birth as 4 BCE :-)
For the astronomical events in various records, I think you've got the logic reversed. We can use celestial mechanics and other astrophysical stuff (see the astronomy site for details) to figure just how long ago comets, eclipses, supernovae &c happened, and then translate that to our dating system. But we could as easily translate to the Chinese, Islamic, Japanese, Roman, or whatever system.
There is no singular event, or main type of event, that aligns ancient with modern calendars.
Ancient calendars tended to be somewhat arbitrary, numbering by years of the current king's reign, or similarly unpredictable things. The Babylonian records of eclipses, planetary conjunctions, and the like allow their calendar to be aligned with certainty because there are so many events that match up.
Aligning other ancient calendars that don't have so many associated astronomical events takes detective work. For example, you might have several possibilities from eclipses of the moon, and be able to pick one from a record of a trading expedition to Babylon that mentions who the king of Babylon was at the time.
Our dating system(s) are not based on astronomical events.
They are based on astronomical cycles. Studies over thousands and thousands of years using more and more accurate instruments has refined scientific knowledge of the length of various astronomical cycles such as the day, the month, and the year.
Thus calendars are designed to be accurate about the length of natural astronomical cycles. Thus the old Roman calendar was replaced by the Julian Calendar that started on 1 January 45 BC, and the Julian Calendar was replaced by the Gregorian Calendar in which Thursday, 4 October 1582 was followed by Friday, 15 October 1582.
In most dating systems the years are numbered from the years of various historical events, not astronomical events.
And this is the very briefest of summaries in answer to your question.
The AD/BC or CE/BCE system of counting the years is not going to be changed because of a discovery of astronomical dates for events in ancient history long before the birth of Christ. But it could be replaced by a different dating system counting events from many centuries earlier.
In Chinese legend and history there are many dates going back to almost 3,000 BC almost 5000 years ago - to the accession of Fuxi in 2952 BC, for example, that would be about 4,969 years before 2017. But there is serious disagreement in various sources about the dates of various events, disagreement that gets smaller and smaller in more recent centuries until 841 BC.
The Gonghe Regency was in 841 to 828 BC, between the exile of King Li of Zhou and the ascension of his son King Xuan of Zhou. Sima Qian, the Grand historian of the Han dynasty, was able to date events back year by year with confidence back to the beginning of the Gonghe Regency in 841 BC.
The Chinese Government sponsored the Xia-Shag-Zhou Chronology Project to put the earlier Chinese chronology on a firmer footing.
Their methods and results are not accepted by all historians.
They put the beginning of the legendary Xia Dynasty in about 2070 BC instead of the traditional 2205 BC, the beginning of the Shang Dynasty in about 1600 BC instead of the traditional 1766 BC, the overthrow of Shang by Zhou in 1046 BC instead of the traditional 1122 BC, etc., etc.
I once read a book in the University of Pennsylvania library that attempted to reconstruct the proper dates of ancient Chinese history.
I don't remember much, but I think that he found an astronomical event, probably an eclipse, said to have happened during the reign of the Yellow Emperor, that seemed to match with an eclipse calculated to have happened during the period that he dated the reign of the Yellow Emperor to. Modern historians mostly believe the Yellow Emperor was a god transformed by later legend into a early Chinese ruler.
So if I remember it correctly, and if he figured it out correctly, he might have accurately dated the reign of the Yellow Emperor - which should be some time during the 3rd millennium BCE - about two thousand years earlier than the earliest historical dates considered completely accurate.
Traditional dates in traditional accounts of Chinese history usually start with the accession of the Yellow Emperor in 2697 or 2698 BCE. In the early 20th century Chinese nationalist Liu Shipei created the Yellow Emperor Calendar, counting the years since the traditional birth of the Yellow Emperor in 2711 BCE.
When the Chinese Republic was proclaimed on January 2, 1912, Sun Yat-Sen said it was the 12th day of the 11th month of the year 4609 (counting from the traditional date of the accession of the Yellow Emperor in 2698 BCE), but from now on it would be year one of the Chinese Republic.
Since years are already sometimes counted from the reign of the Yellow Emperor, if historians ever agree on a certain and undisputable date for his reign (even though most believe he was imaginary) and for the eclipse in it, then a modified version of a Yellow Emperor calendar with corrected dates could become common, since most or all recorded historical events would be after the reign of the Yellow Emperor.
Thus a calendar firmly anchored in an astronomical event could theoretically come into use in the future.