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Why is there a 29 February ? By Hôtel★★★ Restaurant gourmand Coco Lodge Majunga

Julian calendar, multiple 400, celestial mechanics : Why is there a 29 February ?

Leap years are the easiest found by the Romans to imperfectly coordinate the schedule for the duration of the solar year, i.e. on the time interval for the Sun, view of the Earth, Returns to the same position by following the rhythm of the seasons (for example between two equinoxes spring or between two summer solstices).

A solar year lasts about 365,25 days. To compensate for this difference, superposing one day after the 28 February every four years. The leap year, introduced by Jules Caesar in 46 BC. with the reform of the calendar Julian and renewed in the Gregorian calendar, used yet, has seen its calculation rules evolve.

Between – 46 and 1582, When the Julian calendar was in effect, a year was leap if it were a multiple of four. What happening leap years every four years, without exception.
En 1582, the introduction of the Gregorian calendar has refined the calculation of leap years by adding the exception of century years : These must be multiples of 400 to be leap. This rule was introduced to remove three years leap all the 400 years (1600 is a leap year, 1700, 1800 and 1900 are not). Why ? Because a solar year lasts in reality 365,2421904 days. Without this exception rule, There were too many leap years, producing an advance of 3 days all the 400 years.

Celestial Mechanics is complex, It is never bent to the regularity of the human calendar. Advance is actually 3,124 days all the 400 years. Therefore, delete one day all the 3 230 years if it wishes to remain synchronous with the revolution of the earth around the Sun.

A year is not what you think
Did you know that even the solar year (about 365,25 days) does not correspond to a complete revolution of the earth around the Sun ? It is indeed shorter 20 minutes from a complete revolution, whose duration is called sidereal year.
Why ? Because a solar year is a time interval following the rhythm of the seasons and is related to the inclination of the Earth's axis, not at his position States around its orbit. The earth rotates around an axis inclined to 23,26 degrees to the plane of the ecliptic (the plane in which it revolves around the Sun). But this move also axis : This is what is called the precession of the equinoxes. The axis of rotation of the Earth describes, such a router, a circular in motion 25 772 about years.

by Hôtel★★★ Restaurant gourmand Coco Lodge Majunga