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Posidonius calculated the Earth's circumference by reference to the position of the star Canopus.As explained by Cleomedes, Posidonius observed Canopus on but never above the horizon at Rhodes, while at Alexandria he saw it ascend as far as 7 + 1 ⁄ 2 degrees above the horizon (the meridian arc between the latitude of the two locales is actually 5 degrees 14 minutes).
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).
Equatorial diameter of Earth 20.004 Mm Length of a meridian on Earth (distance between Earth's poles along the surface) [37] 40.075 Mm Length of Earth's equator: 10 8: 100 Mm: 142.984 Mm Diameter of Jupiter: 299.792 Mm Distance traveled by light in vacuum in one second (a light-second, exactly 299,792,458 m by definition of the speed of light ...
Earth's rotation period relative to the fixed stars, called its stellar day by the International Earth Rotation and Reference Systems Service (IERS), is 86,164.0989 seconds of mean solar time , or 23 h 56 m 4.0989 s. [2] [n 10] Earth's rotation period relative to the precessing or moving mean March equinox (when the Sun is at 90° on the ...
British media also frequently uses the football pitch for equivalent purposes, although soccer pitches are not of a fixed size, but instead can vary within defined limits (100–130 yd or 91.4–118.9 m long, and 50–100 yd or 45.7–91.4 m wide, giving an area of 5,000 to 13,000 sq yd or 4,181 to 10,870 m 2).
The basic unit of length in the imperial and U.S. customary systems is the yard, defined as exactly 0.9144 m by international treaty in 1959. [2] [5] Common imperial units and U.S. customary units of length include: [6] thou or mil (1 ⁄ 1000 of an inch) inch (25.4 mm) foot (12 inches, 0.3048 m) yard (3 feet, 0.9144 m)
Finding the geodesic between two points on the Earth, the so-called inverse geodetic problem, was the focus of many mathematicians and geodesists over the course of the 18th and 19th centuries with major contributions by Clairaut, [5] Legendre, [6] Bessel, [7] and Helmert English translation of Astron. Nachr. 4, 241–254 (1825).
For comparison, Earth's Moon is even less elliptical, with a flattening of less than 1/825, while Jupiter is visibly oblate at about 1/15 and one of Saturn's triaxial moons, Telesto, is highly flattened, with f between 1/3 and 1/2 (meaning that the polar diameter is between 50% and 67% of the equatorial.