NavList:

Incidentally, I was recently updating the Delta-T values in my celestial navigation spreadsheet. For dates between 500 BC and AD1955* (inclusive), I used the polynomials from NASA's eclipse website. These calculations include a year zero. However, most historic dates are given in either the Gregorian or Julian calendars ... neither of which have a year zero. So, when I originally designed my spreadsheet, I apparently decided to simply omit the year zero.

Hindsight being 20/20, I corrected this by doing what I should have done in the first place: I simply renamed the 'astronomical' year zero as the Julian** year 1 BC. None of that really matters much, though. The problem only affected the years before AD 1, a time at which we can only guess what the value of Delta-T was based on dodgy eclipse reports. And the difference between years was only twenty-two seconds at the maximum, and that is only between the years 499 BC and 500 BC; the difference decreasing to ten seconds between the years 2 BC to 1 BC.

The 'new and improved' version of my spreadsheet will appear on my website as soon as I feel like going through all of the rigamarole of updating it.

Cheers!

Sean C.

* I don't use the terms "CE" and "BCE" because I think their invention was entirely pointless. Most people know what "BC" and "AD" mean. And, after all, I don't know of anyone lobbying to change the names of the days of the week, so as to accomodate anyone who doesn't believe in Norse mythology.

** My spreadsheet uses the Julian calendar for all dates before 15 October, 1582. As you do.