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:

“He who would do good to another must do it in *Minute* Particulars:

General Good is the plea of the scoundrel, hypocrite, and flatterer,

For Art and Science cannot exist but in minutely organized Particulars.”

—William Blake (1757–1827)

“You say that you are my judge; I do not know if you are; but take good heed not to judge me ill, because you would put yourself in great peril.”

—Joan Of *Arc* (c.1412–1431)