# Definition:Angle/Unit/Second

< Definition:Angle | Unit(Redirected from Definition:Second of Arc)

## Definition

The **second (of arc)** is a measurement of plane angles, symbolized by $''$.

- $1''$ is defined as $\dfrac 1 {60}$ of a minute of arc, or $\dfrac 1 {3600}$ of a degree of arc.

## Historical Note

The division of the **degrees** into $60$ and $3600$ subdivisions originates from the Babylonians, who used a sexagesimal (base $60$) system for the purposes of mathematics and astronomy.

## Linguistic Note

The word **second**, in the context of the measurement of time and of angle, derives from the fact that it was originally specified as a **second minute part of an hour** or of a **degree of arc**.

The **minute** had already been defined as a **minute part of an hour**.

The use of the word **second** in English, in this specific context, started near the end of the $16$th century.

## Sources

- Weisstein, Eric W. "Arc Second." From
*MathWorld*--A Wolfram Web Resource. http://mathworld.wolfram.com/ArcSecond.html