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All the time units that appear natural to man are caused by astronomical phenomena: The year by Earth's orbit around the Sun and the resulting run of the seasons, the month by the Moon's movement around the Earth and the change of the Moon phases, the day by Earth's rotation and the succession of brightness and darkness.
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www.maa.mhn.de/Scholar/times.html
www.maa.mhn.de/Scholar/times.html
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Both assumptions are simplifications that lead to deviations from the true astronomical facts. The true beginning of spring happens some time between March 19, 8 o'clock and March 21, 20 o'clock UT. Consideration of the true lunar orbit leads to time differences of up +/- 0.7 days with respect to a circular orbit.
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www.maa.mhn.de/Scholar/calendar.html
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Chapter 2 of the most recent Explanatory Supplement to the Astronomical Almanac [ref 1] gives an extensive summary of time standards and a list of original literature references. The kinds of time typically encountered in astronomy are briefly described below.
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www.cv.nrao.edu/~rfisher/Ephemerides/times.html
www.cv.nrao.edu/~rfisher/Ephemerides/times.html
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GMT on 1918-03-19 Although the term GMT was not explicitly used, the standard time for legal purposes in the United States specified by 15USC261 (the Calder Act) was defined to be based on the mean astronomical time of meridians spaced at 15-degree intervals west of Greenwich;
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www.ucolick.org/~sla/leapsecs/timescales.html
www.ucolick.org/~sla/leapsecs/timescales.html
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Then, as Venusian gravity pulled it back, it would have again sped by the planet—but this time not so far out into space. Eventually, as the tidal forces between the two bodies increased during this strange celestial courtship, ... *The only exception: Uranus, whose backward rotation is an astronomical mystery...
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www.time.com/time/magazine/article/0,9171,942474,00.htm...
www.time.com/time/magazine/article/0,9171,942474,00.html?promoid=googlep
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Astronomical times ... Astronomical Information ... Astronomical Time Keeping...
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www.ecben.net/calendar.shtml
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Fortunately, I am just one of the many amateurs that have so far attempted and did managed to produce astronomical time-lapse animations.
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www.astrosurf.com/cidadao/animations.htm
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Astronomical Time Calculations ... Julian Day is a linear count of days starting on January 1, 4713 BC and is commonly used for astronomical calculations. The Julian Day starts at Noon Universal Time (UT) hence at 0h UT the Julian day is some whole number + 0.5.
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www.go.ednet.ns.ca/~larry/orbits/jsjdetst.html
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Definition of Astronomical time in the Online Dictionary. Meaning of Astronomical time. Pronunciation of Astronomical time. Translations of Astronomical time. Astronomical time synonyms, Astronomical time antonyms. ... The dramatic successes in the development of astronomical time scales receive lots of emphasis,
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www.thefreedictionary.com/Astronomical+time
www.thefreedictionary.com/Astronomical+time
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