Concurrent (Easter)

A concurrent was the weekday of 24 March in the Julian calendar counted from 1 to 7, regarding 1 as Sunday. It was used to calculate the Julian Easter during the Middle Ages. It was derived from the weekday of the first day of the Alexandrian calendar during the 4th century, 1 Thoth (29–30 August), counting Wednesday as 1 (see Planetary hours#History). Therefore, the following 5 Thoth was a Sunday and the following 28 Phamenoth (24 March Julian) [= 208 Thoth ≡ 5 Thoth mod 7] was also a Sunday.^[1][2] It was first mentioned by Dionysius Exiguus in 525 in his Latin version of the original Alexandrian Church's Greek computus.^[3] The insertion of the sixth epagomenal day (29 August Julian) immediately before 1 Thoth was compensated for by the bissextile day (24 February Julian) inserted six months later into the Julian calendar.

The widely used post-Bedan solar cycle (first year 776), which repeats every 28 years, had concurrents of

1 2 3 4 6 7 1

2 4 5 6 7 2 3

4 5 7 1 2 3 5

6 7 1 3 4 5 6.

It skips a concurrent every four years due to a bissextile day in the Julian calendar a month earlier.^[4][5] The Sunday after the next Luna 14 was Easter Sunday (see Computus#Julian calendar). The concurrent is not used by the Gregorian Easter.