solar time

solar time

      time measured by Earth's rotation relative to the Sun. Apparent solar time is that measured by direct observation of the Sun or by a sundial. Mean solar time, kept by most clocks (clock) and watches (watch), is the solar time that would be measured by observation if the Sun traveled at a uniform apparent speed throughout the year rather than, as it actually does, at a slightly varying apparent speed that depends on the seasons. The difference between mean and apparent solar time is known as the equation of time. This is usually expressed as a correction, never exceeding 16 minutes, that is added to or subtracted from apparent solar time to determine mean solar time. The real Sun and the imaginary “mean Sun,” from which mean solar time is measured, may be as much as 16 minutes apart because during the course of the year the apparent motion of the real Sun against the background of the stars (the ecliptic) alternately slows down and speeds up. There are two reasons for this. First, the Earth's orbit is not exactly circular, and the Earth moves in it at slightly different speeds in different seasons. Second, the Earth's axis is tilted relative to the plane of the Earth's orbit.

      Since 1972 the time in common use has been based on a combination of solar and atomic times (atomic time); it is called Coordinated Universal Time. Its second is the second of atomic time, while its epoch is kept by periodic adjustment, within 0.9 second of mean solar time. See also Universal Time.

Jonathan D. Betts
 

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Universalium. 2010.

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Look at other dictionaries:

  • Solar time — Solar So lar, a. [L. solaris, fr. sol the sun; akin to As. s[=o]l, Icel. s[=o]l, Goth. sauil, Lith. saule, W. haul,. sul, Skr. svar, perhaps to E. sun:F. solaire. Cf. {Parasol}. {Sun}.] 1. Of or pertaining to the sun; proceeding from the sun; as …   The Collaborative International Dictionary of English

  • solar time — Time as measured by what appears to be the daily transit of the sun, caused by the rotation of the earth. 52 Am J1st Time § 2. See local sun time; mean solar time; standard time; sun time or standard …   Ballentine's law dictionary

  • Solar time — On a prograde planet like the Earth, the sidereal day is shorter than the solar day. At time 1, the Sun and a certain distant …   Wikipedia

  • solar time — noun : time either apparent or mean indicated by the sun : time expressed in units of mean solar time * * * solar time see under ↑time • • • Main Entry: ↑solar solar time Time reckoned by the sun, real or mean • • • Main Entry: ↑time * * * …   Useful english dictionary

  • solar time — noun the local time based on a solar day the mean time between successive noons Syn: local solar time, mean time …   Wiktionary

  • Solar Time —   The period marked by successive crossing of the earth s meridian by the sun; the hour angle of the sun at a point of observance (apparent time) is corrected to true (solar) time by taking into account the variation in the earth s orbit and rate …   Energy terms

  • solar time — saulinis laikas statusas T sritis Standartizacija ir metrologija apibrėžtis Astronominis laikas, pagrįstas sauline para – laiko tarpu tarp dviejų gretimų vienavardžių vidutinės atogrąžinės Saulės kulminacijų. atitikmenys: angl. solar time vok.… …   Penkiakalbis aiškinamasis metrologijos terminų žodynas

  • solar time — time defined by the position of the sun (when the sun reaches its highest point in the sky then it is noon) …   English contemporary dictionary

  • mean solar time — n. time based on the mean sun: used as the basis for standard time because it has exactly equal divisions: also mean time …   English World dictionary

  • apparent solar time — tikrasis saulinis laikas statusas T sritis Standartizacija ir metrologija apibrėžtis Laikas, pagrįstas tikrąja sauline para – laiko tarpu tarp dviejų Saulės skritulio centro kulminacijų tame pačiame Žemės dienovidinyje. atitikmenys: angl.… …   Penkiakalbis aiškinamasis metrologijos terminų žodynas

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