mean solar day


: the interval between successive transits of a given meridian of longitude by the mean sun
The confusion wasn't resolved for good until 1884, when an international time conference in Washington, D.C., replaced the old-fashioned solar day with the mean solar day—a legal fiction in which the daily fluctuations are averaged out, enabling us to enjoy the blessings of a uniform 24-hour day all year long.Jon Vara

Examples of mean solar day in a Sentence

Recent Examples on the Web For much of the twentieth century, the second was based on a nineteenth-century standard derived from astronomical calculations: 1/86,400 of a mean solar day. Tom Vanderbilt, Harper’s Magazine , 13 Mar. 2023 The mean solar day, to smooth out inconsistencies, is derived from the movement of an idealized, hypothetical sun. Tom Vanderbilt, Harper’s Magazine , 13 Mar. 2023 In the 19th century, scientific institutions worked to define the second in astronomical terms, and in the 1940s an international agreement defined the second as 1⁄86,400 of a mean solar day. Jay Bennett, Popular Mechanics, 24 Mar. 2017

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'mean solar day.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History

First Known Use

1810, in the meaning defined above

Time Traveler
The first known use of mean solar day was in 1810

Dictionary Entries Near mean solar day

Cite this Entry

“Mean solar day.” Dictionary, Merriam-Webster, Accessed 1 Mar. 2024.

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