mean sun
American Heritage Dictionary:
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mean sun
n.
A hypothetical sun defined as moving at a uniform rate along the celestial equator at the mean speed with which the real sun apparently moves along the ecliptic, used in computing the mean solar day.
Wiley Book of Astronomy:
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mean sun
A fictitious body that moves eastward in a circular orbit along the celestial equator (see celestial sphere), making a complete circuit with respect to the vernal equinox in a tropical year. It is the moving point chosen in defining mean solar time.
McGraw-Hill Dictionary of Aviation:
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mean sun
An imaginary body which is assumed to travel around the equinoctial at a constant rate, completing one orbit in the same time that the earth takes to complete one orbit around the ecliptic. Because of the elliptical shape of the earth’s orbit, the apparent angular velocity of the sun we see is not constant; hence, the days as indicated by the apparent travel of the true or apparent sun are not of uniform length. To make the solar day of uniform length, astronomers have invented the mean sun, a fictitious body imagined to move at a uniform rate along the celestial equator, making a complete circuit from west to east in one year.
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American Heritage Dictionary
The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.
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Wiley Book of Astronomy
Copyright © 2004 by Wiley-Blackwell. Wiley and the Wiley logo are registered trademarks of John Wiley & Sons, Inc. and/or its affiliates in the United States and other countries. Used here by license. Read more
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