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In astronomy, the rotation period or spin period [1] of a celestial object (e.g., star, planet, moon, asteroid) has two definitions. The first one corresponds to the sidereal rotation period (or sidereal day), i.e., the time that the object takes to complete a full rotation around its axis relative to the background stars (inertial space).
A dial or ring indicating the numbers 1 to 29 or 30 indicates the moon's age: a new moon is 0, waxes become full around day 15, and then wanes up to 29 or 30. The phase is sometimes shown by a rotating globe or black hemisphere, or a window that reveals part of a wavy black shape beneath.
up to one Sun or Moon diameter (about 0.5° or 30') every 2 minutes; up to one diameter of the planet Venus in inferior conjunction (about 1' or 60") about every 4 seconds; 2,000 diameters of the largest stars per second; Star trail and time-lapse photography capture diurnal motion blur. The apparent motion of stars near the celestial pole ...
The March equinox itself precesses slowly westward relative to the fixed stars, completing one revolution in about 25,800 years, so the misnamed "sidereal" day ("sidereal" is derived from the Latin sidus meaning "star") is 0.0084 seconds shorter than the stellar day, Earth's actual period of rotation relative to the fixed stars. [3]
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).
NASA wants to come up with an out-of-this-world way to keep track of time, putting the moon on its own souped-up clock. Because there's less gravity on the moon, time there moves a tad quicker ...
A lunar 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.
Image credits: Ross Burgener Meanwhile, for Dr. Brandon, the most beautiful natural phenomenon is the northern lights, whereas the most fascinating is the diel vertical migration.