si·​de·​re·​al sī-ˈdir-ē-əl How to pronounce sidereal (audio)
: of, relating to, or expressed in relation to stars or constellations : astral

Example Sentences

Recent Examples on the Web Called sidereal time, the measurement calculates the length of a day by comparing the earth's rotation to the stars. Aaron Pressman, Fortune, 12 Apr. 2017 One tweet, in particular, has birthed a fair number of inky astronauts floating across a sidereal arm. Jesse Lichtenstein, New York Times, 15 June 2017 With this definition, a sidereal year is something like 365.256363 solar days. Rhett Allain, WIRED, 29 Feb. 2012

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'sidereal.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

Word History


Latin sidereus, from sider-, sidus star, constellation

First Known Use

1612, in the meaning defined above

Time Traveler
The first known use of sidereal was in 1612


Dictionary Entries Near sidereal

Cite this Entry

“Sidereal.” Dictionary, Merriam-Webster, Accessed 4 Dec. 2022.

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