A small unit of angular measurement that equal to 1/3600 of a degree and 1/60 of an arc minute. Astronomers measure separations in the sky using degrees with 180 degrees equal to the angular separation between the Northern and Southern Celestial poles.

Jupiter has a maximum apparent diameter of 50 arc seconds. For comparison, the apparent diameter of the Sun and Moon are both approx. 0.5 degrees, which is equal to 30 arc minutes or 1800 arc seconds.