How the date for Easter is calculated

So, When is Easter?

In 1582, Pope Gregory XIII decreed that a new calendar be used. This Gregorian calendar has, over the centuries, replaced most other calendars and nowadays it is used practically everywhere. The main reason for the introduction of this new calendar was that calculating the date of Easter proved problematic.
This is a portrait of Pope Gregory XIII, who in 1582 decreed that a new calendar be used. The Gregorian calendar, which over the centuries has replaced most other calendars, was based on a reform of the way the date of Easter was calculated.

This is a portrait of Pope Gregory XIII, who in 1582 decreed that a new calendar be used. The Gregorian calendar, which over the centuries has replaced most other calendars, was based on a reform of the way the date of Easter was calculated.

Unlike Christmas or All Saints' Day, Easter – the celebration of the resurrection of Jesus Christ – is a moveable feast, which means that its date is not fixed to a particular day of the calendar year but instead changes from year to year.

In early Christianity, different parishes would celebrate Easter on different days. In 325, the Council of Nicaea therefore fixed the procedure for determining the date of Easter Sunday. Easter Sunday would henceforth fall on the first Sunday after the first full Moon of spring (in the northern hemisphere).

1582 was actually ten days short of a full year.

To ensure that the first day of spring, which had been set to 21 March by the Council of Nicaea, would actually coincide with the equinox again, Pope Gregory XIII ordered the advancement of the calendar by ten days in 1582. In some Roman Catholic countries, Thursday, October 4, 1582 was therefore directly followed by Friday, October 15, 1582.

Determining the date of Easter is still very complicated, however, as like its predecessors, the Gregorian calendar is based on the solar year of 365 days whereas Easter is defined in relation to the (full) Moon. A large number of medieval mathematicians worked on calculating the date of Easter. Today, we use the slightly modified formula developed in 1800 by mathematician and astronomer Carl Friedrich Gauss to calculate the calendar date.

According to this formula, Easter falls on a Sunday between March 22 and April 25. This year, the Easter Bunny will be hiding the eggs on April 12.


German Aerospace Center
» print article
Related articles:
This widely reproduced woodcut was published for the first time in 1888 in Camille Flammarion's book "L'atmosphère". It depicts a man who sticks his head through the firmament in order to behold the workings of the universe.
Learn about astronomy

Why astronomy?

» go to article
An illustration of the Milky Way based on photographs taken by the Spitzer space telescope. It shows our Sun in the side arm called 'Orion Spur', below the light-colored center of the galaxy. The abbreviation 'ly' provides the distance in light years.
Speed is relative

How fast is the Earth moving?

» go to article
Search
Astronomy Software

Redshift Android

Redshift for Android

The award winning Astronomy Software Redshift for Android. » more

Redshift Pro

Redshift Pro - Astronomy for iOS

The most advanced Redshift app » more

Redshift Astronomy

Redshift - Astronomy for iOS

The award winning Astronomy Software Redshift for iPhone, iPod touch and iPad. » more

Redshift Discover Astronomy deutsch

Redshift Compact - Discover Astronomy for iOS

The beginners version of the leading astronomy App Redshift » more

Redshift 8 Premium

Redshift 8 Premium - Download Edition (Multilingua Edition)

Explore the universe from your PC with the award-winning and professional planetarium software - Languages: German, English, French
 » more

Redshift 8 Premium DL deutsch/engl 2

Redshift 8 Premium - Update from older versions

Update from Redshift 7 or older to the current version of the professional planetarium software - Languages: German, English, French
 » more

Redshift 8 Compact

Redshift 8 Compact - Download Edition

The professional planetarium software for beginners » more