Measures of Angle
Angles are usually measured in either degree or radian system. The basic
unit of the radian system is radian (rad), which is 1 / (2 * [pi]) of the
full circle and thus about 57.296 degrees ([pi] = 3.141592...).
A degree (°) is 1 / 360 of the full circle. The degree is divided
into sixty parts, called arc minutes (') and arc minutes further into
sixty parts, called arc seconds (''). So, there are 60 arc seconds in
one arc minute and 3600 arc seconds in one degree. By the rule of
amateur astronomers you can estimate angles in the sky by holding your
fist up in the air with your arm stretched straight forward. Then the
fist appears about 7 or 8 degrees wide. The full moon is about half a
degree (or 30') wide.