Julian Calendar
- Introduced by Julius Caesar in 45 BC to replace the Roman calendar (final form in 8 AD)
- commonly used until late 1500s, Orthodox church in Russia still uses it
- tropical year approximated to 365.25 days with an error of 1 day in 128 years
- Common year is 365 days
- Leap years
- Leap year every fourth year comprised of 366 days
- around 10 BC, it was found that priests in charge of computing calendar added leap years every 3 years
- 45 BC, 42 BC, 39 BC, 36 BC, 33 BC, 30 BC, 27 BC, 24 BC, 21 BC, 18 BC, 15 BC, 12 BC, 9 BC, 8 AD, 12 AD, and every fourth year thereafter until introduction of Gregorian calendar
- disagreement over whether 45 BC was a leap year or not
- no leap years between 9 BC and 8 AD decreed by Augustus in order to make up for surplus leap years
- introduced error of 1 day every 128 years (fixed by Gregorian Calendar)
- 1482, vernal equinox moved (1582-325)/128 days=~10 days backwards so 10 days dropped