The gap between two objects measured in degrees on the sky. Your hand at arm’s length is a handy ruler: the little finger covers about 1°, three fingers 5°, a fist 10°, an outstretched hand about 20°. The two front stars of the Plough are a little more than 5° apart.
ToolsInteractive atlas, Celestial fix
Related terms
- Degree
The basic unit of angle on the sky: a full turn of the horizon is 360°, and there are 90° from horizon to zenith. The full Moon is about 0.5° across; the Plough about 25°. A degree divides into 60 arcminutes.
- Arcminute
One sixtieth of a degree, written ′. The Moon is about 31′ across; a good eye separates two points about 1′ apart, like Mizar and Alcor (12′). Nebulae and galaxies measure a few arcminutes.
- Star hopping
The method of starting from an easy bright star and hopping from star to star, chart in hand, to the target. A finder or Telrad and the known size of its field help. It is slow at first, but it is how you learn the sky.
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