It's April Fools' Day

"Why is April 1 a day to celebrate foolishness?": There's some uncertainty about when and where this bizarre tradition began, but the most accepted explanation traces April Fools' Day back to 16th century France. Up until 1564, the accepted calendar was the Julian calendar, which observed the beginning of the New Year around April. According to "The Oxford Companion to the Year," King Charles IX then declared that France would begin using the Gregorian calendar, which shifted New Year's Day to January 1.