Thirteen Days — Worked Examples
The gap between the Julian and Gregorian calendars is currently thirteen days. It grows by one day at certain century years, and it is pure arithmetic — nothing is hidden in it.
Where thirteen comes from
The reform removed ten days in 1582. Since then the Julian calendar has kept 1700, 1800 and 1900 as leap years while the Gregorian did not, adding one day of difference each time: 10 + 3 = 13. The year 2000 was a leap year in both, so nothing changed then.
Worked example — Nativity
25 December on the Julian calendar corresponds to 7 January on the Gregorian civil calendar. Old-calendar Orthodox Christians are keeping 25 December, on their calendar, on the day the civil world calls 7 January. They are not celebrating a different feast on a different date; they are using a different ruler to measure the same day.
Worked example — Theophany
Theophany, 6 January Julian, falls on 19 January civil. The Old New Year — 1 January Julian — falls on 14 January civil, which is why it is still marked in Russia and Serbia.
It is not permanent
In 2100 the Julian calendar will again keep a leap day the Gregorian will not, and the difference becomes fourteen days. Anyone treating thirteen as a fixed or symbolic number is treating an accumulating arithmetic remainder as though it were a constant.
Against the numerology
The number thirteen here carries no theological content whatever. It was ten days in 1582, eleven in 1752 when Britain changed, twelve through the nineteenth century, thirteen now, fourteen from 2100. Reading significance into the current value requires ignoring the other values.
Citations on this file
Sources
- U.S. Naval Observatory — calendar referenceAccumulated Julian-Gregorian difference by century and the leap-rule arithmetic behind it.https://aa.usno.navy.mil/faq/calendars ↗
Links are pointers for further reading. The claim is what is sourced, not the website.