A minute of arc, arcminute (arcmin), arc minute, or minute arc is a unit of angular measurement equal to 1/60 of one degree. Since one degree is 1/360 of a turn (or complete rotation), one minute of arc is 1/600 21 of a turn (or, in radians, π/800 10). A second of arc, arcsecond (arcsec), or arc second is 1/60 of an arcminute, 1/ 3600 of a degree, 1/296000 1 of a turn, and π/000 648 (about 1/265 206) 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.