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[1] This diagram gives a visual analogue using a square: regardless of the size of the square, the added perimeter is the sum of the four blue arcs, a circle with the same radius as the offset. More formally, let c be the Earth's circumference, r its radius, Δc the added string length and Δr the added radius.
In radar-related subjects and in JTIDS, a data mile is a unit of distance equal to 6,000 feet (1,829 metres; 0.9875 nautical miles; 1.136 miles). An international mile is 0.88 data mile. The speed of light is 299,792,458 metres per second (983,571,056 ft/s), or about one foot per nanosecond .
While debating what became the Land Ordinance of 1785, Thomas Jefferson's committee wanted to divide the public lands in the west into "hundreds of ten geographical miles square, each mile containing 6,086 and 4-10ths of a foot" and "sub-divided into lots of one mile square each, or 850 and 4-10ths of an acre". [9]
Respectively, these square divisions of land are approximately 80 chains (one mile or 1.6 km), 40 chains (half a mile or 800 m), and 20 chains (a quarter mile or 400 m) on a side. The chain is still used in agriculture: measuring wheels with a circumference of 0.1 chain (diameter ≈ 2.1 ft or 64 cm) are still readily available in Canada and ...
The "old English mile" of the medieval and early modern periods varied but seems to have measured about 1.3 international miles (2.1 km). [17] [18] The old English mile varied over time and location within England. [18] The old English mile has also been defined as 79,200 or 79,320 inches (1.25 or 1.2519 statute miles). [19]
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).
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1 square yoctometre (ym 2) 1 ym 2 10 −43 100,000 ym 2: 1 femtobarn [3] 10 −42: 1 square zeptometre (zm 2) 1 zm 2 10 −36: 1 square attometre (am 2) 1 am 2 10 −30: 1 square femtometre (fm 2) 1 fm 2 10 −29 66.52 fm 2: Thomson cross-section of the electron [4] 10 −28 100 fm 2: 1 barn, roughly the cross-sectional area of a uranium ...