Arc minute is an important unit in astronomy since it is an expression that communicates small angles. It is also called minute of arc or minute of angle (MOA), and is a unit of measurement for angles. An arc minute is equal to one sixtieth of a degree, and because one degree is composed of one three hundred sixtieth of a circle, a single minute of arc means 1/21,600 part of the arc when encompassed in a closed circle.

The prime is standard symbol that marks the arc minute, but most people often use the single quote in its stead, especially when ASCII characters are the only ones allowed in encoding. To exemplify, an arc minute is written as 1’. The term ‘arc minute’ is also simplified to arcmin or amin. In addition, prefixes, such as the SI prefixes, are also used to mark much smaller degrees. The milli-arcsecond, in particular, is employed in astronomy and is abbreviated into mas. A star’s parallax, angular diameter, and proper motion are noted using milli-arcseconds, also thousandths of an arcsecond.

Not only is the arc minute useful in astronomy but it is also common in the firearms industry and literature. The precision of rifles are marked using arc minute system, but the industry prefers to call it minute of angle.