So I heard two people chatting on the roadside as I was driving by. "How do they come up with the date for Carnival. " The other person looked very perplexed and responded "I doh know."
Well for those two clueless people, who I hope were not Catholic or children of Catholics,I have news for you.
It all begins with the Jewish Passover festival. Passover starts on the 15th day of the Jewish month of Nissan. This varies by year since the Jewish year is a lunar year and thus differs from the Gregorian calendar. It always falls in the springtime, though (in the Northern Hemisphere).
So now lets move to Easter. Jesus was crucified and laid to rest the day before a special Sabbath, it was a passover sabbath. He rose on the Sunday after. So Easter is now forever linked to Passover.
According to Wiki: The Council of Nicaea (A.D. 325) set the date of Easter as the Sunday following the paschal full moon, which is the full moon that falls on or after the vernal (spring) equinox.
We know that Easter must always occur on a Sunday, because Sunday was the day of Christ's Resurrection. But why the paschal full moon? Because that was the date of Passover in the Jewish calendar, and the Last Supper (Holy Thursday) occurred on the Passover. Therefore, Easter was the Sunday after Passover.
The Church does not use the exact date of the paschal full moon but an approximation, For calculation purposes, the full moon is always set at the 14th day of the lunar month (the lunar month begins with the new moon). Likewise, the Church sets the date of the vernal equinox at March 21, even though it can occur on March 20. Both approximations allow the Church to set a universal date for Easter. Easter cannot fall before March 21 and after April 25th.
So lets go back a bit
The vernal equinox is March 21st
The full moon after the vernal equinox in 2012 is April 6th. A Friday.
Easter Sunday 2012 is then April 8th 2012
Now that you know how Easter gets figured out solve for Ash Wednesday and you have carnival. Ash Wednesday is usually 46 days before Easter Sunday. You need to count the days back.