Calendar conversions

In historical astronomical research often one has to know on what day a particular event happened in various calendars. This page will help in that. Choose a day in one calendar and see the result in all others.

All times are based on local time, based on UT (universal time), but depending on the use one can interpret them as ET (efemeris time) or DT (dynamical time) instead.

Use timezone: hours (+Asia, -America)

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Julian date

JD:

A useful way to count the days and for doing calculations, being independent of months and years breaks or cumbersome hours:minutes:seconds. Started 1 jan 4713 BCE at 12:00 UT (Julian proleptic). Designed to start at noon so that astromers will not be confused by the date change if they observe around midnight.

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Gregorian calendar

year: month (1-12): day:

hours: minutes:

  leap year

day of year:

The calendar currently in use by most countries of the world, and for sure for international trade. Introduced on 15 Oct 1582 in catholic countries in Europe, in the 18th century for most protestant countries, and begin 20th century for some east European countries. The era can be designated by AD (anno domini) of CE (common era).

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Julian calendar

year: month (1-12): day:

hours: minutes:

  leap year

day of year:

The calendar preceeding the Gregorian. Introduced in 46 BCE, but its dates are not sure exactly until the last adjustments made in 8 CE. Extrapolated dates in the past are known as the proleptic calendar. As there is no historical year 0, (that becomes 1 BCE), all negative year calculations need 1 year correction (i.e. use -45 for 46 BCE).

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Almanac for

Roman easter: (Gregorian calendar)

Orthodox easter: (Julian calendar)

Golden number (or Metonic cycle):

Solar cycle:

Dominical letters, Julian: , Gregorian:

Roman indiction:   Epact:

Hebrew calendar

year: month (1-12): day:

hours: parts (chalakiem):

AM (anno mundi)

In the Hebrew calendar the months started with the first sighting of the young moon crescent in Jeruzalem, but were delayed often for 1 or 2 days to avoid conflicts with the sabbat. Rabbi Hillel II developed a formula in the 4th century CE, which has been in use since. The calendar is primarily lunar, but adds a embolismic month from time to time to keep up with the solar cycle, making its average length 365.246822205977908 days.

More info.

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Moslem calendar

year: month (1-12): day:

AH (anno hegira()

hours: minutes:

intercalary year

In the Islamic calendar the months start with the first sighting of the young moon crescent in Mecca. In some months the calculated calendar may be a day off from the real moon. Also the day starts at sunset, here set on the fixed moment of 18:00 local time. Calculations of this hijrī calender, in use since the 11th century CE, may also be off a day in both past and present due to different interpretations of the koran by various groups. The calendar is purely lunar, any solar cycle is ignored, and has 354 (or 355) days.

More info.

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Coptic calendar

year: month (1-12): day:

hours: minutes:

AM (anno martyrum)
leap year

The calendar used for the Coptic church, derived from the old Egyptian calendar. With its 12 months of 30 days followed by 5 or 6 epagomene days it arrives at the average of 365.25 days.

More info.

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