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ephemeris second

American  

noun

Astronomy.

  1. the unit of ephemeris time, defined as a precise fraction of the length of the tropical year 1900.

Etymology

Origin of ephemeris second

First recorded in 1965–70

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.