A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol ′,[1] is a unit of angular measurement equal to 160 of one degree.[2] Since one degree is 1360 of a turn (or complete rotation), one minute of arc is 121600 of a turn. The nautical mile (nmi) was originally defined as a minute of latitude on a spherical Earth, so the actual Earth circumference is very near 21600 nmi. A minute of arc is Ï€10800 of a radian.
A second of arc, arcsecond (arcsec), or arc second, denoted by the symbol ″,[3] is 160 of an arcminute, 13600of a degree,[2] 11296000 of a turn, and Ï€648000 (about 1206181.8) of a radian.
These units originated in Babylonian astronomy as sexagesimal subdivisions of the degree; they are used in fields that involve very small angles, such as astronomy, optometry, ophthalmology, optics, navigation, land surveying, and marksmanship.
To express even smaller angles, standard SI prefixes can be employed; the milliarcsecond (mas) and microarcsecond (μas), for instance, are commonly used in astronomy. For a three-dimensional area such as on a sphere, square arcminutes or seconds may be used.
https://en.wikipedia.org/wiki/Minute_and_second_of_arc
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