A **minute of arc**, **arcminute**, or **minute arc** (**MOA**), is a unit of angular measurement equal to one sixtieth (1⁄_{60}) of one degree (circle⁄_{21,600}), or (π⁄_{10,800}) radians. In turn, a **second of arc** or **arcsecond** is one sixtieth (1⁄_{60}) of one minute of arc. Since one degree is defined as one three hundred and sixtieth (1⁄_{360}) of a rotation, one minute of arc is 1⁄_{21,600} of a rotation. It is used in those fields which require a unit for the expression of small angles, such as astronomy, optometry, ophthalmology, optics, navigation and marksmanship.

The number of square arcminutes in a complete sphere is

or approximately 148,510,660.498 square arcminutes.

The arcsecond is 1⁄_{3,600} of a degree, or 1⁄_{1,296,000} of a circle, or (π⁄_{648,000}) radians, which is approximately 1⁄_{206,265} radian.

To express even smaller angles, standard SI prefixes can be employed; in particular, the **milliarcsecond**, abbreviated **mas**, is used in astronomy.

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### Famous quotes containing the words minute and/or arc:

“At each *minute* we are crushed by the idea and the feeling of time. And there are only two ways to escape this nightmare, Mto forget it: pleasure and work. Pleasure wears us out. Work fortifies us. Let’s choose.”

—Charles Baudelaire (1821–1867)

“If I am not, may God put me there; and if I am, may God so keep me.”

—Joan Of *Arc* (c.1412–1431)