arc second

(arcsec; second of arc) Symbol: ″. A unit of angular measure equal to 1/3600 of a degree. It is used, for example, to give the apparent diameter of objects, the angular separation of binary stars, and the proper motion and annual parallax of stars. An arc minute, symbol: ′, is 60 arc seconds, i.e. 1/60 of a degree. The full Moon is about 30′ in diameter.

Collins Dictionary of Astronomy © Market House Books Ltd, 2006

Mentioned in

aberration
advance of the perihelion
angular measure
annual parallax
arc minute
Cloverleaf
Dumbbell nebula
Egg Nebula
gamma-ray bursts
gravitational lens
Holmberg radius
isoplanatic angle
Jupiter
light-year
long-focus photographic astrometry
magnitude
Mars, oppositions
Mercury
minute of arc

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