VAT 4956 - Should it be dated to 568 BC?

Late Start

Could a Babylonian year start as late as 2^nd May?

Some points to consider:

Not according to Richard A. Parker and Waldo H. Dubberstein in Babylonian Chronology, 626 B.C. – A.D. 45 (Note: There is a more upto date version available). The latest a year starts during this period according to them is April 26^th, just 7 days earlier than May 2^nd.
Between 652 BC and 333 BC (319 years) there are only 29 tablets that can be dated with some certainty by Moon and planet positions, only 12 of these tablets have months names intact. Have a look at the tablet comparison, the months highlighted in green have month names, the ones in amber have been calculated. The empty cells show the information that is missing. You will notice that the information for the whole period is fragmentary.
Since VAT4956 is the only Astronomical tablet that has been dated to the 6^th century BC, there is not enough evidence to be 100% certain when each year began.

The current dating of BM 41985 (LBAT 1413) means that the Babylonian year 747 BC started on 21^st February. This is a month before the Spring Equinox, and potentially two lunar months before the year would be expected to start in later periods.

Then there's basic maths

The JD (julian day number) for 22 April 2022 is 2459692 (Days since November 24, 4714 BC - Wiki )
The JD for 22 April 568 BC is 1514073

There are 945,619 days between these two dates

To get the number of years, divide by the orbital period of the earth (NASA )

Tropical years - 2,589.02
Sidereal years - 2,588.92
Julian years - 2,588.96

The closest is 7 days more than 2589 tropical years. Aren't they the same date? Why are they not full years apart?

If you count 2,589 tropical years from 22 April 568 BC it takes you to JD day 2459684, which is 14 April 2022.

There are several reasons why a Babylonian year won't match up with the current calendar

The precession of the equinox (Wiki ). This accounts for a shift of one day about every 71 years.
The calendar was adjusted by 10 days in 1582 (timeanddate.com )
The Babylonian year fluctuated between 12 or 13 lunar months long. (354-384 days long)

As you can see, if you were to ignore the 10 day calendar adjustment of 1582, 22 April 568 BC would be 12 April 568 BC. The 2 May 588 BC would become 22 April 588 BC. These dates are 26 and 36 days respectively after the spring equinox. As noted above, the start of the year in 747 BC was 21 Feb (11 Feb, if you ignore the calendar adjustment) which is 35 days before the spring equinox.

Conclusion

If we consider the calendar as we understand it today, the argument that a year could start in May, 43 days after the equinox, seems unreasonable. Once you understand that it has been retro-fitted in an attempt to tie multiple dating systems together, and that the 2nd of May is more like the 25th April in todays terms, it sounds more reasonable.