2016 is a Leap year. This means that instead of 365 days, we have an extra day. This situation happens every four years, when the 29th of February is added to the calendar. But many people wonder where the story of the Leap Year comes from and what the real reason is that it exists at each time interval.
February 29th came at the time of the Roman Empire, like emperor Julius Caesar. At that time, the calendar was based on the phases of the Moon, called the Lunar Year, and had 304 days. divided into 10 months - there were no months of January and February - being 6 months with 30 days and the remaining with 31.
But after a lot of studying about the time it took the Earth to make a complete circle around the Sun, it was noticed that the calculation, until then known, was not exact and, therefore, should be redefined. At that time, it was believed that the Earth took 365 days to travel around the Sun and that, at the end of those days, we would have completed a full year.
The Solar Year, which gave way to the Lunar Year, was instituted after adjusting this relationship between the Earth and the Sun. Emperor Julius Caesar demystified the calculation of 365 days and came to the conclusion that this loop actually takes 365 days, five hours, 48 minutes and 46 seconds.
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This difference, therefore, should be compensated somehow, because if we counted only the 365 days, we would lose almost six hours a year. These six hours, in four years, add up to a total of 24 hours, in other words, one day. That's why every four years we have an extra day on the calendar. The Romans then decided that this day should be added to the month of February, as it is the shortest of the year.
The leap year is essential for the cycle of seasons to be well defined. If we didn't add a full day every four years, the seasons would end up out of step with the Christmas in totally different seasons in each place on the planet or the calendar would mark spring and we would be in summer, for example.
How to know if a year is a leap year
To find out if a year will be a leap year, it is enough for it to be divisible by 4. The year 2016, for example, is divisible by 4. Therefore, it is leap. But for centenary years (1900, for example) the rule is that it is divisible by 400 so that the month of February has one more day.