tropical year

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Related to Mean tropical year: solar year

tropical year,

time between successive vernal equinoxesequinox
, either of two points on the celestial sphere where the ecliptic and the celestial equator intersect. The vernal equinox, also known as "the first point of Aries," is the point at which the sun appears to cross the celestial equator from south to north.
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; 365 days, 5 hr, 48 min, 46 sec of mean solar time (see solar timesolar time,
time defined by the position of the sun. The solar day is the time it takes for the sun to return to the same meridian in the sky. Local solar time is measured by a sundial.
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). The tropical year is the basis of the yearyear,
time required for the earth to complete one orbit about the sun. The solar or tropical year is measured relative to the sun and is equal to 365 days, 5 hr, 48 min, 46 sec of mean solar time (see solar time).
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 used in the Gregorian calendarcalendar
[Lat., from Kalends], system of reckoning time for the practical purpose of recording past events and calculating dates for future plans. The calendar is based on noting ordinary and easily observable natural events, the cycle of the sun through the seasons with equinox
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.

tropical year

The interval between two successive passages of the Sun through the vernal equinox, i.e. the time taken by the Sun, in its apparent annual motion, to complete one revolution around the celestial sphere relative to the vernal equinox. It is equal to 365.242 19 days. If the vernal equinox were a fixed point on the celestial sphere the tropical year would be equal to the sidereal year. Precession however produces an annual retrograde motion of the equinoxes amounting to 50.28 seconds of arc relative to the fixed stars. The tropical year is thus about 20 minutes shorter than the sidereal year. Since the seasons recur after one tropical year, the average length of a calendar year should be as close as is practicable to the tropical year.

The tropical year of 1900 was the primary unit of ephemeris time. Use of ephemeris time, and hence of the tropical year, was discontinued in 1984.

Tropical Year

(religion, spiritualism, and occult)

The tropical year (also called the solar year, the seasonal year, the natural year, the equinoctial year, and the astronomical year) is the time it takes the Sun to go from one spring equinox to the next—365 days 5 hours and 48 minutes. Because of the precession of equinoxes, the equinox point changes slightly (when looked at against the background of the stars), making a tropical year shorter than a sidereal year (a “star” year) by a little more than 20 minutes.

Tropical Year

 

the time interval between two successive passages of the sun through the vernal equinox. The tropical year contains 365.242196 mean solar days. It is the basis of the modern calendar; a complete change of seasons occurs during the tropical year. In astronomy the beginning of the tropical year is taken as the moment when the mean longitude of the sun (decreased by 20.5”, the value of the constant of aberration) is 280°. The year measured from this moment is called the Besselian year. Its beginning coincides roughly with the beginning of the calendar year.

tropical year

[′träp·ə·kəl ′yir]
(astronomy)
A unit of time equal to the period of one revolution of the earth about the sun measured between successive vernal equinoxes; it is 365.2422 mean solar days or 365 days 5 hours 48 minutes 46 seconds. Also known as astronomical year.

tropical year

tropical yearclick for a larger image
The period between two successive vernal equinoxes, the time the earth takes to complete one orbit around the sun relative to the first point of Aries. Its length was 365 days 5 h 48 min and 45.19 s in 2000, and it is changing by 0.00000006162 x y days (y in Julian years from 2000), or about 5 milliseconds/year. The tropical year differs from the solar year by 1 part in 26,000, since this is the period of the earth's precession about its rotational axis combined with the precession of the perihelion of the earth's orbit. Also called an astronomical, equinoctial, natural, or solar year. It contains one complete cycle of seasons.