# Minute of arc

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A **minute of arc**, **arcminute**, or **MOA** is a unit of angular measurement, equal to one sixtieth (1/60) of one degree. Since one degree is defined as one three hundred sixtieth (1/360) of a circle, 1 MOA is 1/21600 of the amount of arc in a closed circle, or (π/10800) radians. It is used in those fields which require a unit for the expression of small angles, such as astronomy. The SI symbol for marking the arcminute is the prime (′) (`U+2032`

, `′`

), though a single quote (') (U+0027) is commonly used where only ASCII characters are permitted. One arcminute is written 1′ (or 1*'*). It is also abbreviated as **arcmin** or **amin** or, less commonly, the prime with a circumflex over it ().

The subdivision of the minute of arc is the **second of arc**, or **arcsecond**. There are 60 arcseconds in an arcminute. Therefore, the arcsecond is 1/1296000 of a circle, or (π/648000) radians, which is approximately 1/206265 radian. The symbol for the arcsecond is the double prime (″) (`U+2033`

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

### Human vision

In humans, the ability to resolve a spatial pattern separated by a visual angle of one minute of arc is considered normal visual acuity.^{[1]}

## References

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