2012 is a leap year, with 366 days instead of the usual 365 days.
It was the ancient Egyptians who first figured out that the solar year and the man-made calendar year didn’t always match up.
That’s because it actually takes the Earth a little longer than a year to travel around the Sun — 365 days, 5 hours, 48 minutes, and 46 seconds, to be exact.
Therefore, as the hours accumulated over the centures, an extra day was occasionally added to the calendar, and over time the practice became more or less official.
The Romans first designated February 29 as leap day, but a more precise formula (still in use today) was adopted in the 16th century when the Gregorian calendar fine-tuned the calculations to include a leap day in years only divisible by four – 2012, 2016, 2020, 2024, etc. The Gregorian calendar is closely based on the Julian calendar, which was introduced by Julius Caesar in 45 BC. The Julian calendar featured a 12-month, 365-day year, with an intercalary day inserted every fourth year at the end of February to make an average year of 365.25 days. But because the length of the solar year is actually 365.242216 days, the Julian year was too long by .0078 days (11 minutes 14 seconds).
Following the Gregorian reform, the average length of the year was 365.2425 days, an even closer approximation to the solar year. At this rate, it will take more than 3,000 years for the Gregorian calendar to gain one extra day in error.
Another stipulation ruled that no year divisible by 100 would have a leap year, except if it was divisible by 400. Thus, 1900 was not a leap year … but 2000 was! Go figure.
Thankfully, all this intricate plotting will continue to keep us in tune with the seasons over the next several thousand years.