As early as 325CE it was determined that the pagan festival of Easter would be held on:
- the first Sunday
- after the first full moon
- occurring on or after the vernal equinox.
From that point forward, the easter date depended on the date of the vernal equinox ( the time when the sun crosses the plane of the earth’s equator, making night and day of approximately equal length all over the earth). The Vernal (Spring) Equinox in the Northern Hemisphere is the Autumnal (Fall) Equinox in the Southern Hemisphere and vice versa. From the time the festival was appropriated by religions it depended on the ecclesiastical approximation of 21 March for the vernal equinox.
The earliest date for easter Sunday is 22 March and the latest is 25 April.
Occasionally, in Australia, easter falls around Anzac Day (25 April) meaning that by taking only a few days leave you can arrange a 10 day break. We were able to do this in 2014 when we did the Kalgoorlie Karijini Kennedys Kalbarri trip and the opportunity will present itself in 2019 when we plan to journey to the Nullarbor Plain and Great Victoria Desert.