Arcsecond

"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 ($mas$).