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1. a period of time equal to 3600 seconds; 1/24th of a calendar day
2. Astronomy an angular measurement of right ascension equal to 15° or a 24th part of the celestial equator
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
1. A unit of time equal to 60 minutes, i.e. 1/24 of a day.
2. A unit of angle equal to 15° of arc, i.e. 1/24 of a circle. See right ascension.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006
A unit of time equal to 3600 seconds. Abbreviated h; hr.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.