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Lunar day





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Alunar day is the time it takes for Earth's Moon to complete on its axis one synodic rotation, meaning with respect to the Sun. Informally, a lunar day and a lunar night is each approx. 14 Earth days. The formal lunar day is therefore the time of a full lunar day-night cycle. Due to tidal locking, this equals the time that the Moon takes to complete one synodic orbit around Earth, a synodic lunar month, returning to the same lunar phase. The synodic period is about 29+12 Earth days, which is about 2.2 days longer than its sidereal period.

A full lunar day observed from the Earth, where orbital libration causes the apparent wobble.

Main definition

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Relative to the fixed stars on the celestial sphere, the Moon takes 27 Earth days, 7 hours, 43 minutes, 12 seconds to complete one orbit;[1] however, since the Earth–Moon system advances around the Sun at the same time, the Moon must travel farther to return to the same phase. On average, this synodic period lasts 29 days, 12 hours, 44 minutes, 3 seconds,[1] the length of a lunar month on Earth. The exact length varies over time because the speed of the Earth–Moon system around the Sun varies slightly during a year due to the eccentricity of its elliptical orbit, variances in orbital velocity, and a number of other periodic and evolving variations about its observed, relative, mean values, which are influenced by the gravitational perturbations of the Sun and other bodies in the Solar System.

As a result, daylight at a given point on the Moon lasts approximately two weeks from beginning to end, followed by approximately two weeks of lunar night.

Alternate usage

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Lunar calendars

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In some lunar calendars, such as the Vikram Samvat, a lunar day, or tithi, is defined as 1/30 of a lunar month, or the time it takes for the longitudinal angle between the Moon and the Sun to increase by 12 degrees. By this definition, lunar days generally vary in duration.

See also

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References

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  1. ^ a b "Month". Encyclopædia Britannica. Retrieved 15 April 2015.
  • ^ "Frequency of Tides - The Lunar Day". NOAA. Retrieved 15 May 2019.
  • ^ "This is why lunar colonies will need to live underground".
  • ^ Urrutia, Doris Elin (16 May 2019). "Goodnight, Chang'e-4! China's Probe on Moon's Far Side Naps for Lunar Night". space.com. Future US, Inc. Retrieved 15 November 2019.
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    Last edited on 13 July 2024, at 19:49  





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    This page was last edited on 13 July 2024, at 19:49 (UTC).

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