"Arc Second" is a unit of angular measure, also called the \(\textit{second of arc}\), equal to \(1/60 \; arcminute\). One arcsecond is a very small angle: there are 1,296,000 in a circle. The SI recommends \(\textit{double prime}\) (\(''\)) as the symbol for the arcsecond. The symbol has become common in astronomy, where very small angles are stated in milliarcseconds (\(mas\)).