Last modified on 8th August 2000.

Encyclopædia Galactica

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Measures of angle

Angles are 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 your fist appears about 7 or 8 degrees wide. The full moon is about half a degree (or 30') wide.

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Created by Rami T. F. Rekola