si·​de·​re·​al | \sī-ˈdir-ē-əl, sə-\

Definition of sidereal 

: of, relating to, or expressed in relation to stars or constellations : astral

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Mark Time With the History of Sidereal

In Latin, the word for a star or constellation is sidus. Latin speakers used that word to form desiderare ("from a heavenly body") and considerare ("to think about a heavenly body"), which were adopted into English as desire and consider. Sidereal, another sidus creation, was first documented in English in 1642. Thirty-four years later, an astronomer coined the phrase "sidereal year" for the time in which the earth completes one revolution in its orbit around the sun, measured with respect to the fixed stars. Not surprisingly, other sidereal measurements of time followed, including the sidereal month, the sidereal day, the sidereal hour, and even the sidereal minute.

Examples of sidereal in a Sentence

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, "Data Sheet—Amazon Makes Overdue Price Cuts at Whole Foods," 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, "A Whimsical Wordsmith Charts a Course Beyond Twitter," 15 June 2017 With this definition, a sidereal year is something like 365.256363 solar days. Rhett Allain, WIRED, "Why Is There a Leap Year?," 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.

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First Known Use of sidereal

1612, in the meaning defined above

History and Etymology for sidereal

Latin sidereus, from sider-, sidus star, constellation

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Time Traveler for sidereal

The first known use of sidereal was in 1612

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