View source for Radian

[[File:Radian cropped color.svg|250px|thumb|Definition of a radian]]
[[File:Circle_radians.gif|thumb|250px|right|A radian is a unit of angular measure. A turn in a full circle has an angle of 2π radians.]]

A '''radian''' is a unit of measuring [[angle]]s. It is shown by the symbol "rad" or, less often, <sup>c</sup> (for circular measure). The radian was once an [[SI]] unit, but was done away with in 1995.

A "milliradian" is 1/1000 of a radian.

== Who uses radians? ==
Most people who do mathematics or physics use radians, rather than  [[degree (angle)|degrees]], because some kinds of calculations, mostly in [[trigonometry]] and [[calculus]], are simpler when using radians rather than degrees. 

People who look through a [[telescope]] or [[rifle]] scope often use milliradians to describe distances as seen through it.

This unit of measurement is often used in the universe of the popular video game [[Mass Effect]] in relations to [[Quantum entanglement|physics]].

== Conversion ==
1 radian is equal to about 57.3°. There are 2[[Pi (mathematical constant)|π]] radians (about 6.28 radians) in a full circle. The formula for turning radians to degrees and vice versa is:
:<math>2\pi\mbox{ rad} = 360^\circ</math>
:<math>1 \mbox{ rad} = \frac {360^\circ} {2 \pi} = \frac {180^\circ} {\pi} \approx 57.29577951^\circ </math>

or:

:<math>360^\circ=2\pi\mbox{ rad}</math>
:<math>1^\circ=\frac{2\pi}{360}\mbox{ rad}=\frac{\pi}{180}\mbox{ rad} \approx 0.01745329\mbox{ rad}</math>

we can also say:

:<math>x \mbox{ rad} = \left(\frac{180x}{\pi}\right)^\circ</math>.


{{math-stub}}

[[Category:Angles]]