The plane angle between two radii of a circle which cut off on the circumference an arc equal in length to the radius.
- Secondary SI Unit
- The secondary SI unit for the plane angle is the radian.
|1 degree (°)||=||π/180 radian||1 radian (rad)||=||57.2958 degree (°)|
|1 minute (′)||=||1/60 degree (°)||1 second (")||=||1/60 minute (′)|
|1 grad (or grade)||=||1/100 right angle||right angle||=||π/2 radian (rad)|
The size of an object in the sky can be measured by the angle that it covers when viewed from Earth. The diameter of the full Moon is about one-half of a degree or 30 arcmin.