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tropical year: the period for the Earth to complete one revolution with respect to the equinox. This point is on the intersection of the ecliptic (the plane of the orbit of the Earth) and the plane of the equator (the plane perpendicular to the rotation axis of the Earth). Because of the precession, this points moves slowly backwards along the ecliptic; as a a consequence, the Earth reaches this point before it completes a full orbit as measured in a fixed reference frame. Therefore the tropical year is shorter than the sideral year: its average duration is: |
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tropical year: the period for the Earth to complete one revolution with respect to the equinox. This point is on the intersection of the ecliptic (the plane of the orbit of the Earth) and the plane of the equator (the plane perpendicular to the rotation axis of the Earth). Because of the precession, this points moves slowly backwards along the ecliptic; as a consequence, the Earth reaches this point before it completes a full orbit as measured in a fixed reference frame. Therefore the tropical year is shorter than the sideral year: its average duration is: |
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Julian year: 365.25 days, the average length of the year in the Julian Calendar. |
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Julian year: 365.25 days, the average length of the year in the Julian Calendar. Besselian year: this is a tropical year that starts when the mean Sun reaches the ecliptic longitude of 280 deg. This is always on or close to the 1st day of January. It is named after the 19th-century astronomer and mathematician Friedrich Bessel. An approximate formula to compute the current time in Besselian years from the [Julian day]? is: B = 2000 + (JD - 2451544.53)/365.242189 |
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