second ["] Unit Converter

Definition of second ["] unit

An arcsecond, often called a second of arc, is an angular unit equal to one-sixtieth of an arcminute and one-3,600th of a degree. It measures very small angles and equals π/648,000 radians, approximately 4.848 microradians.

History of second ["] unit

The term second comes from the sexagesimal subdivision system inherited from ancient Babylonian mathematics, in which units were repeatedly divided by sixty. In medieval and early modern astronomy, a degree was divided into minutes, and each minute into seconds, establishing the arcsecond as a practical fine-angle measure. Astronomers adopted it for describing stellar positions and apparent diameters. Its modern symbol, ″, reflects this tradition. The unit became especially important with telescopic astronomy, precision surveying, geodesy, and, later, astrometry, where tiny positional differences required consistent angular notation.

Applications of second ["] unit

Today, arcseconds are used in astronomy to report stellar coordinates, telescope resolution, planetary positions, and the apparent separation of celestial objects. In geodesy and surveying, they express small changes in latitude, longitude, and direction. Imaging systems may specify angular resolution in arcseconds, while astrophysicists use milliarcseconds or microarcseconds for precise stellar motion and distance measurements.

Complete list of second ["] unit conversion