solar day

astronomy

Also known as: sol

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July 16, 2026

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A solar day is the time it takes for the Earth to complete one rotation on its axis relative to the Sun. This is the basis for our common 24-hour day, which is divided into two 12-hour periods: AM (ante meridiem, before noon) and PM (post meridiem, after noon).1

A sidereal day, in contrast, is the time it takes for the Earth to rotate once relative to the background of stars. Because the Earth is also orbiting the Sun, a solar day is about four minutes longer than a sidereal day. The mean solar day is the average length of a solar day, accounting for slight variations throughout the year.12

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day
The apparent solar day is the time between two successive transits of the Sun over the same meridian. Because the orbital motion of the Earth makes the Sun seem to move slightly eastward each day relative to the stars, the solar day is about four minutes longer…
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The apparent solar day is the time between two successive transits of the Sun over the same meridian. Because the orbital motion of the Earth makes the Sun seem to move slightly eastward each day relative to the stars, the solar day is about four minutes longer…
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Mars
Basic astronomical data
6 Martian solar days, called sols. Because of the elliptical orbit, southern summers are shorter (154 Martian days) and warmer than those in the north (178 Martian days). The situation is slowly changing, however, such that 25,000 years from now the northern summers will be the shorter…
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6 Martian solar days, called sols. Because of the elliptical orbit, southern summers are shorter (154 Martian days) and warmer than those in the north (178 Martian days). The situation is slowly changing, however, such that 25,000 years from now the northern summers will be the shorter…
Read More