Easter moon

There’s always a full moon just before Easter – an Easter moon.  By Easter Sunday it will be between one and seven days old.  All this is because the date of Easter Sunday is based on the Jewish lunar calculations for the date of Passover, which is when the “Last Supper” is set.  The history for these calculations is complex, but the present method (as used, for example, for determining public holidays in Australia) is summed up by this:

Easter Day is the Sunday immediately following the first full moon that occurs on or after 21 March.

The charts show the earliest and latest possible dates.

Earliest

Easter is at its earliest when the moon is full on 21 March and it is a Saturday. The Sunday “immediately following” is 22 March.

21 Mar	22 Mar
Sat	Sun	mon	tue	wed	thu	fri	sat
full moon	Easter day

Latest

Easter is at its latest when the moon is full on 20 March.  This is one day short of “on or after 21 March”.

20 Mar . 21 Mar
Full
moon

The next full moon is taken to occur 29 days later (approximately one lunar month), which is 18 April.  If 18 April is a Sunday, then the Sunday “immediately following” is 25 April, which is the latest it can be.

18Apr	19Apr	20Apr	21Apr	22Apr	23Apr	24Apr	25Apr
sun	mon	tue	wed	thu	fri	sat	sun
full moon				Maundy Thursday	Good Friday	holy Saturday	Easter day