![]() ![]() "When the Egyptians adopted this calendar they were aware that there was a problem," says Lowe. The practice of adding extra days to the year is at least as old as these systems. Their 360-day year was nearly a week shorter than our annual journey around the sun. Other ancient calendars, dating to the Sumerians 5,000 years ago, simply divided the year into 12 months of 30 days each. So societies that kept lunar time quickly drifted well out of sync with the seasons due to the 11-day lag. "We've made a calendar that comes close,” Lowe says, "but to make it work you have to do these leap day tricks that have some quirky rules." Ancient timekeeping strategiesĮfforts to make nature's schedule fit our own have been imperfect from the start.Įarly Egyptians (prior to about 3100 B.C.) and other societies from China to Rome once used lunar calendars to track time.īut lunar months average 29.5 days and years only about 354. That's why most of the modern world has adopted the Gregorian calendar and its leap year system to allow days and months to stay in step with the seasons. WATCH: Neil deGrasse Tyson explains the logic behind the leap year, with a brief history in calendars as well. Religious leaders expected feast days to align with certain seasons and lunar phases. ![]() ![]() Ancient Egyptians planted their crops each year on the night when the brightest night star disappeared, while historians in ancient Greece and Rome also relied on the positions of the stars to anchor events in time. Humans have long organized our lives in accordance with what we've observed in the skies. No calendar comprised of whole days can match that number, and simply ignoring the seemingly small fraction creates a much bigger problem than one might suspect. The solar year is approximately 365.2422 days long. ![]() "It all comes down to the fact that the number of Earth's revolutions about its own axis, or days, is not connected in any way to how long it takes for the Earth to get around the sun," says John Lowe, who led the National Institute of Standards and Technology (NIST)'s Time & Frequency Division until his retirement. In February of that year 11 days were 'lost' from the month of September when the Gregorian calendar was adopted by Britain.It's that time again: Saturday, February 29, is a leap day, the calendar oddity that occurs (almost) every four years.įor centuries, attempts to sync calendars with the length of the natural year have sowed chaos-until the concept of leap year provided a way to make up for lost time. The first leap year in modern times in Britain was 1752, according to the Royal Museums Greenwich. Eventually we'd find it would be freezing cold in July, and really hot in December. If we didn't have a leap year the seasons would slowly start to shift. That means a year is rounded down to 365 days, but an extra day is added every four years to make up the time. We have to heave leap years, because it takes the Earth 365.25 days to orbit the sun. Leap years fall every four years to keep the calendar year in synch with the astronomical year. That means that the year 2000 was a leap year, but 1900 wasn't. A good way to remember it is that leap years only happen on years that are divisible by four, except for end-of-century years which must be divisible by 400. The next leap year will fall on February 2024, which means there's another two years until we'll experience a leap year. Were you born on a leap year? Let us know in the comments below ![]()
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