Karkausvuoden

Karkausvuoden, known in English as a leap year, is a year that contains an extra day, February 29th. This addition is made to keep the Gregorian calendar, the most widely used civil calendar, in alignment with the astronomical year. The Earth's orbit around the Sun is not precisely 365 days; it takes approximately 365.2422 days. Without a leap day, the calendar would gradually drift out of sync with the seasons.

The rule for determining a leap year is as follows: a year is a leap year if it is divisible by 4. However, there is an exception: years divisible by 100 are not leap years, unless they are also divisible by 400. For example, 2000 was a leap year because it is divisible by 400, but 1900 was not a leap year because it is divisible by 100 but not by 400.

The concept of a leap year has been implemented in various calendar systems throughout history, with the Gregorian calendar's system being the most sophisticated and widely adopted. The addition of a leap day helps to prevent significant seasonal shifts over long periods. Without this adjustment, summer months would eventually occur in winter and vice versa. Karkausvuoden occurs approximately every four years.