It took Julius Caesar to take the confusion out of the calendar and the politics out of the spring rites of the vernal equinox. All he needed was one extra day every four years to make it happen.
In 45 BC the Julian calendar was introduced and it solved at least two major problems that the Romans had with their previous unwieldy system.
The old Roman calendar was developed around the fact that the sun's orbit around the Earth is 365.24219 days in length. That means its orbit is just a few minutes short of 365 and one-quarter days. Over time, without the addition of a leap day, the calendar gets out of whack with the sun's position in the sky relative to the Earth. That caused huge problems, especially for ancient peoples who wanted to celebrate exactly the end of winter and the first day of spring.
The Romans, and the Greeks before them figured out that the vernal equinox normally took place in and around March 21. They could predict the equinox accurately but without the addition of a leap day every four years, the spring rites had to be held earlier and earlier in the calendar month.
The celebration of spring rites was important to many cultures. The day when there is equal night and day was key to celebrations of ancient Babylonians, Jews, Egyptians, Greeks, Romans and Christians.
The pre-Julian Romans compensated for the discrepancy by occasionally adding entire months to the calendar. This system had political ramifications because the priests in charge of decreeing when the extra days were added were also political figures who wanted to maintain their jobs in office. By adding days they could stay in power for longer lengths of time.
Somewhere in the midst of warring with Egypt and romancing with Cleopatra, Julius Caesar realized that the Egyptians had a somewhat better calendar system that involved adding an extra leap day every fourth year, in February.
The man who figured out the new Julian calendar, which combined the knowledge of Greek, Egyptian and Roman astrologers, is believed to have been Sosigenes of Alexandria.
Imagine the confusion this change caused in 45 BC! Where previously whole months had been added to align the Earth and the Sun, now there was a whole new numbering system to their calendar. Some Romans found that the date of their birth had been changed to a different date that previously had never existed. This wasn't all bad. Some Romans simply celebrated their birth twice, with two different parties in the same year.
When's Easter?
Pope Gregory XIII had problems with the Julian calendar because Easter was gradually being celebrated earlier and earlier. In 1582 he asked his astronomers to fine-tune the Julian calendar. The fix that the Pope came up with meant that most century years, such as 1700, 1800 and 1900 would not be leap years. Only century years divisible by 400, such as 2000, would be leap years.
In those countries that adhere to the Gregorian calendar, 2012 is a leap year and today, February 29 is leap day.
Leap day is a bona fide extra day designed to align us with the sun's movements and to make sure that all is in order for the glorious moment when spring arrives.
So what are you going to do with your extra 24 hours? You could, like the ancient Romans, celebrate an extra birthday. Have a party. Go skydiving. Ice fishing. Touch base with a friend. Clean the kitchen cupboards.
Whatever you do with this extra day, leap to it. Both an ancient Caesar and a medieval-era Pope decreed its existence. There won't be another leap day or leap year until 2016.
Fun facts
• Julius Caesar introduced leap years in 45 BC.
• Julius Caesar was assassinated one year later, in 44 BC but the calendar system named in his honour remained.
• Without a leap day/leap year, our calendars would be off by 24 days after only 100 years.
• There are four million people in the world born on leap day.
• People born on leap day are called leaplings.
• When leaplings enter Feb. 29 as their day of birth on official forms, most computers reject them.
• WestJet, which became a company Feb. 29, 1996, offers discounts on that day to people with leap day birthdays.
• The Chinese calendar is lunisolar, so a leap year in that system has an extra month.
• To ensure that Passover is always in spring, the Hebrew calendar allows for a complicated system of corrections seven times every 19 years.
• Leap day births are rare and in Scotland it's considered bad luck to be born on Feb. 29.
• According to Irish legend, St. Bridget and St. Patrick made a deal allowing women to propose to men on that day. The deal was supposed to strike a balance in the traditional roles between men and women in the same way that leap years did for the calendar.
• Sadie Hawkins Day is associated with leap day.
