Plane Angle

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.

See also: Angles, Complementary Angles, Degree, Goniometer, Grade of a Slope, Inscribed Angle, Minute, pi, Radian, Rotation, Second, Sexagesimal.

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Subjects: Geometry