Fat Tuesday (or Mardi Gras, the French translation) has become synonymous with raucous, hedonistic parties and over-indulgence on every level. It's hard to imagine that the roots of this day actually lie in the Christian calendar.
It is the "last hurrah" before Lent begins the next day or Ash Wednesday. All of the partying done on that day, especially in New Orleans, stops abruptly at midnight. Scores of street sweepers and police send the crowds home to start the solemn and penitent season of Lent.
Fat Tuesday is also known as Carnival, which comes from the Latin words carne and vale or "farewell to the flesh".
Carnival is celebrated around the world, most notably in Rio de Janeiro, Brazil. Early traditions of the day included slaughtering and feasting on a fattened calf.
There are still more names for this day of celebration. It is also referred to in religious circles as "Shrove Tuesday". Shrove is a derivative of "to shrive" or to hear confessions.
The name Pancake Tuesday came about as a result of a long-time custom of making pancakes before Lent began so as to use up fat, eggs and dairy before the fasting and abstinence begins.
We know that Fat Tuesday is the day before Lent begins, the day before Ash Wednesday, but we don't always know when that will be. That's because the timing of Lent is based on the timing of Easter and that, is based on the Sun.
For those of us living above the Equator, the first day of spring is March 21st. This is the spring or Vernal Equinox - or the first day of the year when there is more day than night. Three months later, June 21, the longest day of the year will arrive and summer will begin.
Easter cannot be before March 23rd or after April 25th. This is because it falls on the first Sunday succeeding the first full moon after the Spring Equinox. Lent, then, is the seven-week period (40 weekdays and seven Sundays to be exact) preceding Easter.
Accordingly, Fat Tuesday is 41 weekdays before the first Sunday after the Spring Equinox and after the first full moon of that Equinox. Or you can just plan ahead for the next few years as follows:
February 24, 2009
February 16, 2010
March 8, 2011
February 21, 2012
February 12, 2013
Past that - you'll just have to figure it out yourself.