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Picture of a poster clarifying the difference between a sidereal day and the more conventional solar day Animation showing the difference between a sidereal day and a solar day. Sidereal time ("sidereal" pronounced / s aɪ ˈ d ɪər i əl, s ə-/ sy-DEER-ee-əl, sə-) is a system of timekeeping used especially by astronomers.
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 + 1 ⁄ 2 Earth days, which is about 2.2 days longer than its sidereal period.
27.321661 days [7] (equal to sidereal orbital period due to spin-orbit locking, a sidereal lunar month) 27 d 7 h 43 m 11.5 s: 29.530588 days [7] (equal to synodic orbital period, due to spin-orbit locking, a synodic lunar month) none (due to spin-orbit locking) Mars: 1.02595675 days [3] 1 d 0 h 37 m 22.663 s: 1.02749125 [8] days: Ceres: 0.37809 ...
The TLE format is a de facto standard for distribution of an Earth-orbiting object's orbital elements. A TLE set may include a title line preceding the element data, so each listing may take up three lines in the file, in which case the TLE is referred to as a three-line element set (3LE), instead of a two-line element set (2LE). The title is ...
W1 is the ecliptic longitude of the Moon w.r.t. the fixed ICRS equinox: its period is the sidereal month. If we add the rate of precession to the sidereal angular velocity, we get the angular velocity w.r.t. the Equinox of the Date: its period is the tropical month (which is rarely used). l is the mean anomaly: its period is the anomalistic month.
Timekeeping on the Moon is an issue of synchronized human activity on the Moon and contact with such. The two main differences to timekeeping on Earth are the length of a day on the Moon, being the lunar day or lunar month, observable from Earth as the lunar phases, and the rate at which time progresses, with 24 hours on the Moon being 58.7 microseconds (0.0000587 seconds) faster, [1 ...
Given enough time, this would create a mutual tidal locking between Earth and the Moon. The length of Earth's day would increase and the length of a lunar month would also increase. Earth's sidereal day would eventually have the same length as the Moon's orbital period, about 47 times the length of
Combining these two effects, the net acceleration (actually a deceleration) of the rotation of the Earth, or the change in the length of the mean solar day (LOD), is +1.7 ms/day/cy or +62 s/cy 2 or +46.5 ns/day 2. This matches the average rate derived from astronomical records over the past 27 centuries.