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Earth radius (denoted as R 🜨 or R E) is the distance from the center of Earth to a point on or near its surface. Approximating the figure of Earth by an Earth spheroid (an oblate ellipsoid), the radius ranges from a maximum (equatorial radius, denoted a) of nearly 6,378 km (3,963 mi) to a minimum (polar radius, denoted b) of nearly 6,357 km (3,950 mi).
This is a compilation of symbols commonly used in astronomy, ... Mean anomaly; M o - Mean anomaly at ... R E, R 🜨 - Radius compared to Earth;
The symbol for 99942 Apophis, a near-Earth asteroid discovered in 2004 that attracted interest when initial observations suggested a significant probability of an Earth impact in 2029 (a possibility since eliminated), is much later. It was designed by Denis Moskowitz, who also designed many of the dwarf-planet symbols, at a time when asteroid ...
Earth's rotation period relative to the Sun—its mean solar day—is 86,400 seconds of mean solar time (86,400.0025 SI seconds). [158] Because Earth's solar day is now slightly longer than it was during the 19th century due to tidal deceleration , each day varies between 0 and 2 ms longer than the mean solar day.
A variety of symbols or iconographic conventions are used to represent Earth, whether in the sense of planet Earth, or the inhabited world, or as a classical element.A circle representing the round world, with the rivers of Garden of Eden separating the four corners of the world, or rotated 45° to suggest the four continents, remains a common pictographic convention to express the notion of ...
In the 2nd century CE, Ptolemy estimated the mean distance of the Sun as 1210 times Earth's radius. [36] [37] To determine this value, Ptolemy started by measuring the Moon's parallax, finding what amounted to a horizontal lunar parallax of 1° 26′, which was much too large. He then derived a maximum lunar distance of 64 + 1 / 6 Earth ...
If the impact of Earth's equatorial bulge is not significant for a given application (e.g., interplanetary spaceflight), the Earth ellipsoid may be simplified as a spherical Earth, in which case the geocentric and geodetic latitudes are equal and the latitude-dependent geocentric radius simplifies to a global mean Earth's radius (see also ...
The Earth's radius is the distance from Earth's center to its surface, about 6,371 km (3,959 mi). While "radius" normally is a characteristic of perfect spheres, the Earth deviates from spherical by only a third of a percent, sufficiently close to treat it as a sphere in many contexts and justifying the term "the radius of the Earth".