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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.
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).
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.
The partial lunar eclipse shone bright across a portion of the planet this week. Unlike a total lunar eclipse, a partial lunar eclipse occurs when the sun, moon and Earth are in an imperfect ...
The Independent’s picture editors bring you the best photography from all corners of the planet
Features include locations of the sun and moon in the zodiac, Julian calendar, Gregorian calendar, sidereal time, GMT, local time with daylight saving time and leap year, solar and lunar cycle corrections, eclipses, local sunset and sunrise, moon phase, tides, sunspot cycles and a planetarium including Pluto's 248-year orbit and the 25 800-year ...
But there's another system, too, called sidereal astrology. An astrologer explains. Skip to main content. Sign in. Mail. 24/7 Help. For premium support please call: 800-290-4726 more ...
The exact length has been variously defined as either that of a solar day or of a sidereal day. [ 1 ] [ 2 ] [ 3 ] Astronomical days were historically used by astronomers (in contrast most commonly to solar days), but since the Industrial Revolution this usage has generally fallen out of favor, in order to avoid confusion with more conventional ...