What is the exact length of a calendar year?
A year is the time it takes for the Earth to complete one revolution around the sun. Specifically, this period is 365.242199 days (365 days, 5 hours, 48 minutes, 46 seconds). The fact that a year is not comprised of a whole number of days has posed challenges to calendar-makers throughout the millennia. For instance, the ancient Egyptians, Romans, and Greeks used calendars with 365 days. This calendar, however, was off by an entire day approximately every four years. A big improvement was made with the Julian calendar, crafted by Julius Caesar (100-44 B.C.) in 46 B.C. The Julian calendar, which was 365.25 days long, inserted an extra day, or “leap day,” every fourth year. Even with that adjustment, the Julian calendar was off by 11 minutes and 14 seconds per year. By the mid-1500s that error had accumulated so that the Julian calendar was 10 days ahead of the Earth’s…
