Minute of arc

A minute of arc, arcminute, or MOA is a unit of angular measurement, equal to one sixtieth (1/60) of one degree. Since one degree is defined as one three hundred sixtieth (1/360) of a circle, 1 MOA is 1/21600 of the amount of arc in a closed circle, or (&pi;/10800) radians. It is used in those fields which require a unit for the expression of small angles, such as astronomy. The SI symbol for marking the arcminute is the prime (&#8242;), though a single quote (') (U+0027) is commonly used where only ASCII characters are permitted. One arcminute is written 1&#8242; (or 1&#39;). It is also abbreviated as arcmin or amin or, less commonly, the prime with a circumflex over it ($$\hat{'}$$).

The subdivision of the minute of arc is the second of arc, or arcsecond. There are 60 arcseconds in an arcminute. Therefore, the arcsecond is 1/1296000 of a circle, or (&pi;/648000) radians, which is approximately 1/206265 radian. The symbol for the arcsecond is the double prime (&#8243;). To express even smaller angles, standard SI prefixes can be employed; in particular, the milliarcsecond, abbreviated mas, is sometimes used in astronomy.

Human vision
In humans, the ability to resolve a spatial pattern separated by a visual angle of one minute of arc is considered normal visual acuity.