Mean solar day

From Glossary of Meteorology
The printable version is no longer supported and may have rendering errors. Please update your browser bookmarks and please use the default browser print function instead.



mean solar day

The interval of time between two successive meridional transits of the "mean sun," an imaginary point moving with such constant angular velocity along the celestial equator as to complete one annual circuit in a time period exactly equal to that of the apparent (true) sun in its annual circuit.

The mean solar day is 86 400 seconds, or 1.0027379 sidereal day. This modification of the apparent solar day was devised as a means of smoothing the irregularities observed in apparent relative motion of sun and earth; the equation of time defines the difference between the two. Outside astronomical circles, the mean solar day is the day in common use, but since it is reckoned from noon to noon, it has been modified to the civil day for practical use.


Copyright 2024 American Meteorological Society (AMS). For permission to reuse any portion of this work, please contact [email protected]. Any use of material in this work that is determined to be “fair use” under Section 107 of the U.S. Copyright Act (17 U.S. Code § 107) or that satisfies the conditions specified in Section 108 of the U.S.Copyright Act (17 USC § 108) does not require AMS’s permission. Republication, systematic reproduction, posting in electronic form, such as on a website or in a searchable database, or other uses of this material, except as exempted by the above statement, require written permission or a license from AMS. Additional details are provided in the AMS Copyright Policy statement.