Wikipedia reservations on 763 BCE eclipse dating.

An interesting quote from the above article in Wikipedia:

"Accepting June 15, 763 BC as the date of the eclipse means that the same
year Nisan 1 must have begun on March 20, that is 8 or 9 days before the
spring equinox falling that year on March 28/29.
"Nevertheless, historians so far have been unwilling to make any changes in
the traditional Assyrian chronology as that in turn would affect Babylonian,
Egyptian, Israelite and other chronologies as well. The assumption is that
the Assyrian calendar did not necessarily follow the rules of the Babylonian
calendar so that Nisan 1 may have been occasionally declared before the
vernal equinox, as was the case with the Hebrew calendar. However, this
theory is unsupported and seems very unlikely, as Jews had their own,
religious reasons to start their year before the spring equinox: the barley
harvest had to begin about the time of the Passover. Moreover, the earliest
known date for Nisan 1 among the ancient Jews is March 19, 459 BC (as
calculated from double dated Elephantine Papyri),[2] that is 6 or 7 days
before the vernal equinox. This means that March 20, 763 BC would have been
the earliest occurrence of Nisan 1 (in relation to the spring equinox)
documented in the whole ancient history, which casts further doubts upon the
763 BC eclipse choice."

The above reference isn't entirely accurate as there were rare occasions
from NB calendars where the year did begin before the equinox. But using
the VAT4956 as a reference, the Full Moon does not occur until some 9 days
after the equinox, whereas in 763 BCE the Full Moon occurs only 4 days after
the equinox. Comparison of the relative New Moons shows that in 568 BCE
the New Moon occurred on the 23rd of March, just 4 days before the vernal
equinox on the 27th. In 763 BCE the New Moon occurs on the 19th of March,
some 9 days before the vernal equinox on the 28th. Thus even when the New
Moon was just 4 days before the equinox, in 568 BCE the Babylonians still
introduced a 13th month.

ANOTHER PROBLEM: There is another problem as well. The 763 BCE eclipse was
part of an exeligmos pattern of eclipses that were successive every 54 years
and 1 month in the same region. If the eclipse mentioned in the equinox is
presumed to have been predicted, which is why it would have been mentioned
in the eponym list, which is a civil record, then the astronomers would have
been aware of the 54-year-1-month rule. That means one would assume if the
763 BCE eclipse was customarily dated to month 3, then the previous eclipse
in the series in 817 BCE would have been dated to month 2. This is
optional in both cases since the full moon does occur after the vernal
equinox, though just one day after in 817 BCE, a strong argument against
this. However, the previous eclipse in this series in 871 BCE cannot be
optionally dated to month 1. That's because the Full Moon occurs a day
before the equinox on the 28th, the equinox occurs on the 29th. Therefore,
the exeligmos pattern of 54-years-1-month would be out of sync if 763 BCE
were dated to the 3rd month since there is no choice but to date the 871 BCE
eclipse in month 12 or 13.

871 BCE April 12th Month 13 only

817 BCE May 13th Month 1 or 2

763 BCE June 15th Month 2 or 3

709 BCE July 17th Month 3 or 4

If the Assyrians were calculating the exeligmos series precisely and
consistently every 54 years and 1 month later from 871 BCE, then June 15,
763 would fall in order as month 2 not month 3. The July 17, 709 BCE
eclipse would fall naturally in month 3.

As noted, the Assyrians were aware of the 54-year-1-month pattern and
predicted eclipses based on that pattern, only they were not seen every 54
years and 1 month later. That is, not until this rare series of eclipses
that occurred in the same region for these eclipses. In this case, three
major eclipses were seen in a row in the series. This was rare and

The 871 BCE eclipse was not likely seen in Assyria. It was a very minor
partial eclipse. The 817 BCE eclipse though was around 50% so definitely
would have been seen. That was followed by a total eclipse in 763 BCE, the
second in the series they would have surely seen. But seeing two eclipses
in a row would have established the presumption that a third in the series,
perhaps of equal intensity as the first, another 50% eclipse might occur.
It did! If anticipated it would have become a major civic event explaining
why it is mentioned in the eponym. However, in order to calculate the
correct month, they have to date it 54 years and 1 month after the previous
one, and if that series started back in 871 BCE then month 3 is the 709 BCE
eclipse, not 763 BCE.

Below is a graphic of the intensities of the three eclipses involved:

SUMMARY: The 763 BCE eclipse has come into question because it uses an
exceptional dating practice of beginning the year prior to the vernal
equinox. However, this eclipse is part of a series of successive eclipses
that occurred in Assyria, each 54 years and 1 month apart. It his
particular series was being observed as early as 871 BCE, then to be
consistent with the 54-year-1-month intervals would mean the 763 BCE eclipse
must fall in month 2 and not month three. That's because the 871 BCE
eclipse cannot optionally be dated to month one, but must be dated to month
13. In that case, the 709 BCE eclipse following that pattern of
54-years-1-month would fall in month 3. That is, 871 in month 13, 817 in
month 1, 763 in month 2, 709 in month 3, etc. Further, since the 709 BCE
eclipse was the third major eclipse seen in this series in Assyria, there is
a very strong indication that it was predicted and would explain why it was
mentioned in the Assyrian eponym, which is a brief civic journal of major
events for each year. Thus comparatively the 709 BCE eclipse is far more
likely the original eclipse reference than the 763 BCE eclipse

Lars Wilson