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[sahy-deer-ee-uh l] /saɪˈdɪər i əl/
adjective, Astronomy.
determined by or from the stars:
sidereal time.
of or relating to the stars.
Origin of sidereal
1625-35; < Latin sīdere(us) of, belonging to the stars (sīder-, stem of sīdus star, constellation + -eus adj. suffix) + -al1
Related forms
sidereally, adverb
nonsidereal, adjective
unsidereal, adjective Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2017.
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Examples from the Web for sidereal
Historical Examples
  • Could an ordinary watch be turned into a sidereal watch by moving the regulator?

    A Text-Book of Astronomy George C. Comstock
  • So the constitution of the sidereal universe is just like that of the bodies which we call material.

    Urania Camille Flammarion
  • He has come to the bounds of the sidereal system—seen to the confines of the universe.

  • Not only nebul are probably unstable, but also many of the sidereal systems.

    The Asteroids Daniel Kirkwood
  • In one day, a man may go out of the town of Kbul to where snow never falls, or he may go, in two sidereal Fol.

    The Bbur-nma in English Babur, Emperor of Hindustan
  • It is more than Napoleonic; it is continental, interplanetary, sidereal!

    The Arena Various
  • sidereal Year, the period during which the earth makes a revolution in its orbit with respect to the stars.

    The Nuttall Encyclopaedia Edited by Rev. James Wood
  • But because that has gone from the sidereal chart, it does not follow that there is no such place.

  • Thus the maturity of a sidereal system may be judged from the disposition of the component parts.

  • The instrument was turned in answer to these questions to the sidereal heavens.

British Dictionary definitions for sidereal


of, relating to, or involving the stars
determined with reference to one or more stars: the sidereal day
Derived Forms
sidereally, adverb
Word Origin
C17: from Latin sīdereus, from sīdus a star, a constellation
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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Word Origin and History for sidereal

also siderial, 1630s, "star-like;" 1640s, "of or pertaining to the stars," earlier sideral (1590s), from French sidereal (16c.), from Latin sidereus "starry, astral, of the constellations," from sidus (genitive sideris) "star, group of stars, constellation," probably from PIE root *sweid- "to shine" (cf. Lithuanian svidus "shining, bright"). Sidereal time is measured by the apparent diurnal motion of the fixed stars. The sidereal day begins and ends with the passage of the vernal equinox over the meridian and is about four minutes shorter than the solar day, measured by the passage of the sun over the meridian.

Online Etymology Dictionary, © 2010 Douglas Harper
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sidereal in Science
  1. Relating to the stars or constellations.

  2. Measured with respect to the background of fixed stars instead of the Sun.

The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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