For pranksters and joke lovers, there is no better day than April 1. Often called April Fools' Day, it is the one day of the year when light-hearted tricks are not only expected but also welcomed by all. Some believe the fun holiday began in 1582 when the world transitioned from the Julian calendar, which celebrated the New Year on the last week of March, to the current Gregorian calendar. Those unaware of the change, or refusing to accept the January 1 start date, were often mocked and had jokes played on them on or around the old New Year. Others speculate the holiday began as a joyful way to welcome spring.