Leap Year
2024 is a leap year, which is a year with an extra day in February. And today, February 29, is leap day. The concept of leap day has existed for more than 2,000 years. It is necessary to keep our calendar in alignment with the Earth's revolutions around the sun.
It takes the Earth approximately 365.242189 days – or 365 days, 5 hours, 48 minutes, and 45 seconds – to circle once around the sun. Without an extra day on February 29 nearly every four years, we would lose almost six hours every year. After only 100 years, a calendar without leap years would be off by approximately 24 days. Seasonal days such as the spring equinox or the winter solstice would shift in relation to the months in the calendar and in a few centuries, August would become a spring month. Leap days fix the misalignment by giving the earth additional time to complete a full circle around the sun.
The Roman general Julius Caesar implemented the first leap day in his Julian Calendar, which he introduced in 45 BC. A leap day was added every four years but a problem with measurement led to increasing discrepancy over the course of several centuries. The Gregorian calendar, which is what we use today, reformed the concept in 1582 by eliminating leap years in century years that weren’t divisible by 400. Therefore, the years 1600 and 2000 were leap years but 1700, 1800, and 1900 were not.
The Gregorian calendar is not perfect. There’s still a 30-second drift every year. Even with that, the calendar won’t be off for more than a day for another 3,300 years.
