mean solar day


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

First Known Use of mean solar day

1810, in the meaning defined above

Learn More About mean solar day

Time Traveler for mean solar day

Time Traveler

The first known use of mean solar day was in 1810

See more words from the same year

Dictionary Entries Near mean solar day

means of support

mean solar day

mean something to (someone)

See More Nearby Entries 

Statistics for mean solar day

Cite this Entry

“Mean solar day.” Dictionary, Merriam-Webster, Accessed 29 Jun. 2022.

Style: MLA
MLACheck Mark Icon ChicagoCheck Mark Icon APACheck Mark Icon Merriam-WebsterCheck Mark Icon


Test Your Vocabulary

Name That Food

  • a-light
  • Name these cookies!
True or False

Test your knowledge - and maybe learn something along the way.

Universal Daily Crossword

A daily challenge for crossword fanatics.

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!