arcminute

Arcminute, abbreviated arcmin and denoted by the prime symbol (′), is a unit of angular measurement equal to one sixtieth of a degree. It corresponds to 60 arcseconds and equals pi/10800 radians, about 0.000290888 radians. It is used to express small angles on the celestial sphere as well as in geographic coordinates on Earth.

In practice, arcminutes are a subdivision of degrees. Therefore, 1 degree = 60 arcminutes, and 1 arcminute = 1/60 degree. Conversely, 1 arcminute is 60 arcseconds. This system is commonly used in astronomy to describe angular sizes and separations of objects, and in geography to denote minutes of latitude or longitude.

In astronomy, arcminutes are suitable for moderate to small angular scales. For example, the Moon’s apparent diameter is about 31 arcminutes and the Sun’s about 32 arcminutes. The Andromeda Galaxy spans roughly 3 degrees on the sky (about 180 arcminutes). When higher precision is required, arcseconds or radians are preferred, but arcminutes remain convenient for many observational descriptions and catalog references.

In geographic use, arcminutes are part of the degree-minute-second notation for latitude and longitude, often written as degrees and minutes (and sometimes seconds) of arc. Practical measurement and discussion commonly reference arcminutes in telescope catalogs, sky surveys, and mapping.

Note that arcminutes are distinct from minutes of time; the latter are a separate unit used in timekeeping.