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 of, minute and/or arc:

“I make this in a warring absence when

Each ancient, stone-necked *minute of* love’s season

Harbours my anchored tongue....”

—Dylan Thomas (1914–1953)

“Well, there’s no one at all, they do be saying, but is deserving of some punishment from the very *minute* of his birth.”

—Augusta, Lady Gregory (1859–1932)

“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)