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Besides the day of 24 hours (86,400 seconds), the word day is used for several different spans of time based on the rotation of the Earth around its axis. An important one is the solar day, the time it takes for the Sun to return to its culmination point (its highest point in the sky). Due to an orbit's eccentricity, the Sun resides in one of ...
Earth-based: the day is based on the time it takes for the Earth to rotate on its own axis, as observed on a sundial [citation needed]. Units originally derived from this base include the week (seven days), and the fortnight (14 days). Subdivisions of the day include the hour (1/24 of a day), which is further subdivided into minutes and seconds ...
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.
Known affectionately to scientists as the "boring billion," there was a seemingly endless period in the world's history when the length of a day stayed put. The time when a day on Earth was just ...
A definition of a terrestrial time standard was adopted by the International Astronomical Union (IAU) in 1976 at its XVI General Assembly and later named Terrestrial Dynamical Time (TDT). It was the counterpart to Barycentric Dynamical Time (TDB), which was a time standard for Solar system ephemerides, to be based on a dynamical time scale ...
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 ...
The Earth is tilted approximately 23.5 degrees on its axis, and each solstice is dictated by the amount of solar declination, or "the latitude of Earth where the sun is directly overhead at noon ...
The equation of time is the east or west component of the analemma, a curve representing the angular offset of the Sun from its mean position on the celestial sphere as viewed from Earth. The equation of time values for each day of the year, compiled by astronomical observatories, were widely listed in almanacs and ephemerides. [2] [3]: 14