Current Julian Period

Scaliger’s Julian Period combines three repeating cycles: the 15-year indiction cycle, the 19-year lunar cycle, and the 28-year solar cycle. Because 15, 19, and 28 are pairwise coprime and their product is 7,980, every possible combination occurs exactly once in a Julian Period.

The two Cycle Year fields identify the same year: one as a Julian Period year and the other as a BC/AD year in the Julian calendar. Julian Period year 1 is 4713 BC, and year 7,980 is AD 3267. The converter uses the proleptic Julian calendar throughout and never uses the Gregorian calendar. Internally, the conversion is:

astronomical year = Julian Period year − 4713

Astronomical year 0 corresponds to 1 BC, −1 to 2 BC, and +1 to AD 1. The displayed BC/AD calendar therefore has no year zero.

For Julian Period year Y, each cycle position is ((Y − 1) mod cycle length) + 1. Selecting one position in each cycle reconstructs the unique period year with that combination. The 15-year indiction completes the unique three-cycle combination but does not change the epact or dominical letter.

The Dionysian epact follows Dionysius’s alternative rule for the position within the 19-year cycle: subtract 1, multiply by 11, divide by 30, and retain the remainder. In symbols: 11 × (19-year cycle − 1) mod 30. A remainder of zero is the nulla epact; this converter displays it as 0.

The dominical letter is determined by the 28-year solar cycle. The letters A–G mark successive dates beginning with A on 1 January; the dominical letter identifies the dates that are Sundays. Julian leap years have two letters: the first applies before the leap-day adjustment and the second after it.

The go-to buttons select four reference years. A highlighted button means that its year is currently displayed.