arcsecond

The term 'arcsecond' is a modern scientific compound formed by combining 'arc', referring to a segment of a circular curve, with 'second', a unit of division. This follows the ancient Babylonian sexagesimal (base-60) system of angular measurement, inherited by Greek and later European astronomy. In this system, a degree is divided into 60 minutes (Latin pars minuta prima, "first small part"), and each minute is further divided into 60 seconds (pars minuta secunda, "second small part"). Thus, an 'arcsecond' literally means the "second small part of an arc," precisely defining an extremely small angle used primarily in astronomy and geodesy.

Structure: arc + second - arc: From Latin arcus (bow, arch, curve). In this compound, it denotes a segment of a curved line or circle. - second: From Latin secundus (following, next), via the division of time and angle into primary (first) and secondary (second) parts. Here, it refers to the second division (1/60) of a minute.