Tropical year
See also: Year
The tropical year is defined like the time interval in which the average longitude of the Sun on its Orbite connects, that is the ecliptic , grows of 360°.
This definition - in its contemporary meaning in modern science - is due to the French astronomer André Danjon, 1890 - 1967.
With the beginning of the year 2000, i.e. with the Time 2000.0, the duration of the tropical year was of 365,242 190.517 days, is 365 D 5 H 48 min 45,2606 S, according to the measurement taken by the French astronomer Pierre Bretagnon (1942 - 2002). (ref. Paris-Meudon Observatory;)
The duration of the tropical year decreases slightly in time, currently from approximately 0,53 S per century.
The tropical year is “the year of the returns of the seasons” and it constitutes the base of the solar calendars.
Note that, up to one recent time, one generally confused the tropical year and “ the year vernal ”, i.e. the time interval which runs out between two successive passages of the Sun to the vernal equinox.
Explanation
The tropical year corresponds to the periodicity of the Saison S, and is determined like them following some the variations height of the apparent trajectory of the Sun (ecliptic) above the horizon, whose depends the average sunning on the place considered.
The Solstice S of summer and winter correspond roughly to the extreme values of the angle formed by the axis of rotation and the direction Ground-Sun.
Variations of the duration of the tropical year
The duration of the tropical year is slightly variable (reduction of 0,53 S per century) because of various gravitational interactions between the Earth, the the Moon and the others Planet S of the Solar system.
See too
Related articles
- Calendar year
- sidereal Year
External bond
- Glossary of the Observatory of Paris
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