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  2. Planetary hours - Wikipedia

    en.wikipedia.org/wiki/Planetary_hours

    As each day is divided into 24 hours, the first hour of a day is ruled by the planet three places down in the Chaldean order from the planet ruling the first hour of the preceding day; [2] i.e. a day with its first hour ruled by the Sun ("Sunday") is followed by a day with its first hour ruled by the Moon ("Monday"), followed by Mars ("Tuesday ...

  3. Sidereal time - Wikipedia

    en.wikipedia.org/wiki/Sidereal_time

    A mean solar day (what we normally measure as a "day") is the average time between local solar noons ("average" since this varies slightly over a year). Earth makes one rotation around its axis each sidereal day; during that time it moves a short distance (about 1°) along its orbit around the Sun.

  4. Unit of time - Wikipedia

    en.wikipedia.org/wiki/Unit_of_time

    1.44 minutes, or 86.4 seconds. Also marketed as a ".beat" by the Swatch corporation. moment: 1/40 solar hour (90 s on average) Medieval unit of time used by astronomers to compute astronomical movements, length varies with the season. [4] Also colloquially refers to a brief period of time. centiday 0.01 d (1 % of a day) 14.4 minutes, or 864 ...

  5. Day - Wikipedia

    en.wikipedia.org/wiki/Day

    A sidereal day is about 4 minutes less than a solar day of 24 hours (23 hours 56 minutes and 4.09 seconds), or 0.99726968 of a solar day of 24 hours. [7] There are about 366.2422 stellar days in one mean tropical year (one stellar day more than the number of solar days). [8]

  6. Rotation period (astronomy) - Wikipedia

    en.wikipedia.org/wiki/Rotation_period_(astronomy)

    Synodic rotation period (mean Solar day) Apparent rotational period viewed from Earth Sun [i] 25.379995 days (Carrington rotation) 35 days (high latitude) 25 d 9 h 7 m 11.6 s 35 d ~28 days (equatorial) [2] Mercury: 58.6462 days [3] 58 d 15 h 30 m 30 s: 176 days [4] Venus: −243.0226 days [ii] [5] −243 d 0 h 33 m: −116.75 days [6] Earth: 0. ...

  7. Astronomical unit - Wikipedia

    en.wikipedia.org/wiki/Astronomical_unit

    Comparison of the ephemeris positions with time measurements expressed in Barycentric Dynamical Time (TDB) leads to a value for the speed of light in astronomical units per day (of 86,400 s). By 2009, the IAU had updated its standard measures to reflect improvements, and calculated the speed of light at 173.144 632 6847 (69) au/d (TDB).

  8. Synodic day - Wikipedia

    en.wikipedia.org/wiki/Synodic_day

    The longest and shortest synodic days' durations differ by about 51 seconds. [4] The mean length, however, is 24 hours (with fluctuations on the order of milliseconds), and is the basis of solar time. The difference between the mean and apparent solar time is the equation of time, which can also be seen in Earth's analemma.

  9. Venus - Wikipedia

    en.wikipedia.org/wiki/Venus

    Because of the retrograde rotation, the length of a solar day on Venus is significantly shorter than the sidereal day, at 116.75 Earth days (making the Venusian solar day shorter than Mercury's 176 Earth days — the 116-day figure is close to the average number of days it takes Mercury to slip underneath the Earth in its orbit [the number of ...