A minute of arc or arcminute (MOA)'s a unit of angular measurement, equal to one sixtieth (1/60) of one degree. Since one degree's defined as one three hundred sixtieth (1/360) of a circle, 1 minute of arc's 1/21,600 of the amount of arc in a closed circle. It's used in those fields which require a unit for the expression of small angles, such as astronomy or marksmanship. There're 148,510,800 square arcminutes in a complete sphere. Symbols, abbreviations and subdivisions The standard symbol fo… (More on Arcsecond)