Tropical Year
The tropical year or year equinoctial is defined as the time interval in which the mean longitude of the Sun in its orbit apparent (the ecliptic ) increases from 360 . This definition - in its contemporary meaning in modern science - is due to the French astronomer Andr Danjon (1890-1967).
In early 2000, that is to say to the Epoch 2000.0 , the duration of the tropical year was 365.242 190 517 days or 365 days 5 hours 48 minutes 45.2606 seconds , according measurement by the French astronomer Pierre Bretagnon (1942 - 2002). The duration of the tropical year slightly decreased over time, currently about 0.53 s per century.
The tropical year is "the year of return of the seasons" and is the basis of solar calendars Explanation The tropical year is the periodicity of the seasons , and is determined as they follow the variations in the height of the apparent trajectory of the Sun ( ecliptic ) above the horizon , which depends on the average sunshine of that place. The solstices of summer and winter extreme values correspond approximately to the angle between the axis of rotation and the Earth-Sun direction. Solar radiation (Text rotated 90 ) The duration of the tropical year is slightly variable (decrease of 0.53 s per century) due to various gravitational interactions between Earth, the Moon and other planets of the solar system. Winter solstice Summer solstice 
Legend: Axis of Earth
Arctic Circle | Tropic of Cancer | Ecuador | Tropic of Capricorn | Antarctic Circle
Changes in the length of the tropical year
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