There are not 365 Days in a Year

There are roughly 365.25 days in a year. That is an increase of ¼ of a day each year that is not shown on the calendar. After 4 years of additional ¼ days the calendar is ahead by 1 full day. A day is added to the calendar every 4 years to compensate for this additional day that has accumulated. The year that occurs every 4 years with the additional day (February 29) is called a LEAP YEAR.

Even 365.25 days per year is not entirely accurate because that is about 5½ minutes too long each year. That is the reason why every century is not a leap year unless it can be divided by 400 as well as by 4. This means that 3 years is lost every 400 years to compensate for the extra 5½ minutes per year. The "400 rule" was introduced by Pope Gregory in 1582.  Therefore the year 2000 was a leap year but the year 2100 is not a leap year because 2100 is divisible by 4 but it is not divisible by 400.