ArcminuteOne 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.
ArcsecondOne sixtieth of an arcminute, or 1/3,600 of a degree, written ″: the apparent size of a coin about 2.5 cm wide seen from about 5 km away. Jupiter spans 30 to 50″, Mars 25″ at most. Seeing in western Europe often spreads stars over 2 to 3″.
Angular distanceThe 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.