n.
Time required for the Earth to travel once around the Sun, slightly less than 365 1 4 days.
This fractional number makes necessary the periodic adjustment of days in any calendar that is to be kept in step with the seasons. In the Gregorian calendar , a common year contains 365 days, and every fourth year is a leap year of 366 days except for any year that is divisible by 100 but not divisible by 400 (e.g., 1900 was not a leap year).