The way the calendar works, Easter Sunday can take place no later than April 25. The date for Easter Sunday 2011 is April 24.
The modern calendar allows for 35 possible dates for Easter Sunday, between March 22 and April 25. The earliest Easter date is a rarity, having last taken place in 1818 and it won't happen again for another 200 years. A late Easter is also rare, with the last April 25 Easter Sunday in 1943 and the next in 2038.
As the Press-Enterprise notes, "For many people, Sunday will be the latest Easter in their lifetimes."
So how is the date determined?
The First Council of Nicaea in 325 A.D. determined Easter would take place the first Sunday after the "Paschal full moon," which follows the Northern Hemisphere's vernal (spring) equinox.
Looking ahead, Easter Sunday 2012 falls on April 8, and the one after that is slated for March 31.