Synonyms: minute of arc, second of arc. Subdivisions of an angle, analogous to subdivisions of time: Sixty arcseconds correspond to one arcminute; sixty arcminutes (or 3600 arcseconds) correspond to one degree. A right angle has 90 degrees, or 5400 arcminutes, or 324000 arcseconds.

To denote fractions of these units, a prefix is added in the usual way – for instance, one thousandth of a second of arc is a millisecond of arc.