Arc Second (″)
The arc second, symbol ″, is equal to 1/60 of an arc minute or 1/3,600 of a degree, so there are 3,600 arc seconds in one degree and 1,296,000 arc seconds in a full circle. Like the arc minute, it has deep roots in Babylonian astronomy and has remained vital for precision measurement. Arc seconds are heavily used in astronomy to describe angular distances between stars or the apparent size of celestial objects. In geodesy and cartography, arc seconds are used to define coordinates with extreme accuracy. Modern telescopes and space missions often measure distances in arc seconds, reflecting the importance of this unit in advancing scientific discovery.
Arc Minute (′)
An arc minute (′) represents one-sixtieth of a degree, so a full degree contains 60 arc minutes and a complete circle has 21,600 arc minutes. Its origins trace back to ancient astronomers in Babylon and Greece, who needed finer subdivisions of the degree for celestial observations and mapping. Today, arc minutes are still fundamental in fields such as astronomy, navigation, and land surveying. They are commonly used in geographic coordinate systems—latitude and longitude—where they offer a more precise measurement than whole degrees.