This source seems to suggest that the January 1st was a 'political compromise':
According to Kevin Tobin Julius Caesar wanted to start the year on the vernal equinox or the winter solstice, but the Senate, which traditionally took office on January 1st, the start of the Roman civil calendar year, wanted to keep January 1st as the start of the year, and Caesar yielded in a political compromise.
So our current calendar isn't really synchronized with anything: just when some ancient Roman big whigs got together every year. So, that's definitely not fit for the terran computational calendar start date.
As for the equinox, what year do you think we should sync that to? I'll see how that might work with terran computational algorithm....:
vernal equinox 1970: 6825600 seconds (79 days) after the UNIX Epoch.
Hmmm... not as round as -10 days, but maybe... What about 1977?
vernal equinox 1977: 228528000 TAI seconds (2645 TAI days) after the UNIX Epoch & 88 days after the 1977 TAI redefinition... easy to remember I guess. But then, how would leap seconds be handled? If they aren't handled then the day slowly drifts from midnight losing a full hour after about 4-5000 years (which is a pretty long time, so maybe leap seconds shouldn't really be accounted for). And maybe the terran computational calendar should simply keep in sync with TAI and then define year bases in some other way to handle leap seconds?
Calendar Epochs, in my opinion, are the most difficult things to pick when designing a calendar. I've had tons of trouble with it over the years.
And, as far as the beginning of units goes, I still like the thought of them changing when everything is in it's most dormant state.
Can you or anyone think of any other neutral accurately measurable Epochs?