A minute of arc or arcminute (MOA) is a unit of angular measurement, equal to one sixtieth (1/60) of one degree. WordNet Search - 3.0 Since one degree is defined as one three hundred sixtieth (1/360) of a circle, 1 minute of arc is 1/21,600 of the amount of arc in a closed circle. It is used in those fields which require a unit for the expression of small angles, such as astronomy or marksmanship. The number of square arcminutes in a complete sphere is » 4 pi left(frac, MOA 290.8882087 µra… (More on Arcsecond)