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Related to solar time: Equation of time
sequential arrangement of all events, or the interval between two events in such a sequence. The concept of time may be discussed on several different levels: physical, psychological, philosophical and scientific, and biological.
..... Click the link for more information. defined by the position of the sun. The solar dayday,
period of time for the earth to rotate once on its axis. The ordinary day, or solar day, is measured relative to the sun, being the time between successive passages of the sun over a stationary observer's celestial meridian.
..... Click the link for more information. is the time it takes for the sun to return to the same meridian in the sky. Local solar time is measured by a sundialsundial,
instrument that indicates the time of day by the shadow, cast on a surface marked to show hours or fractions of hours, of an object on which the sun's rays fall.
..... Click the link for more information. . When the center of the sun is on an observer's meridian, the observer's local solar time is zero hours (noon). Because the earth moves with varying speed in its orbit at different times of the year and because the plane of the earth's equator is inclined to its orbital plane, the length of the solar day is different depending on the time of year. It is more convenient to define time in terms of the average of local solar time. Such time, called mean solar time, may be thought of as being measured relative to an imaginary sun (the mean sun) that lies in the earth's equatorial plane and about which the earth orbits with constant speed. Every mean solar day is of the same length. The difference between the local solar time and the mean solar time at a given location is known as the equation of time. Tables used by navigators list the equation of time for different times of year so that an observer can calculate his mean solar time from his local solar time (found by determining the sun's hour anglehour angle,
in astronomy, a coordinate in the equatorial coordinate system. The hour angle of a celestial body is the angular distance, expressed in hours, minutes, and seconds (one hour equals 15 degrees), measured westward along the celestial equator from the observer's
..... Click the link for more information. ). Mean solar time is the basis for civil timecivil time,
local time based on universal time. Civil time may be formally defined as mean solar time plus 12 hr; the civil day begins at midnight, while the mean solar day begins at noon.
..... Click the link for more information. and standard timestandard time,
civil time used within a given time zone. The earth is divided into 24 time zones, each of which is about 15° of longitude wide and corresponds to one hour of time. Within a zone all civil clocks are set to the same local solar time.
..... Click the link for more information. .
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1. Short for mean solar time.
2. Short for apparent solar time.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006
solar time[′sō·lər ′tīm]
Time based on the rotation of the earth relative to the sun.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.