Square degree

A square degree (deg2) is a non-SI unit measure of solid angle. Other denotations include sq. deg. and (°)2. Just as degrees are used to measure parts of a circle, square degrees are used to measure parts of a sphere. Analogous to one degree being equal to ⁠π/180⁠ radians, a square degree is equal to (⁠π/180⁠)2 steradians (sr), or about ⁠1/3283⁠ sr or about 0.3046 msr (millisteradian). The whole sphere has a solid angle of 4π sr, which is approximately 41253 deg2: 4 π ( 180 π ) 2 deg 2 = 360 2 π deg 2 = 129 600 π deg 2 ≈ 41 252.96 deg 2 . {\displaystyle 4\pi \left({\frac {180}{\pi }}\right)^{2}\,{\deg }^{2}={\frac {360^{2}}{\pi }}~{\deg }^{2}={\frac {129\,600}{\pi }}~{\deg }^{2}\approx 41\,252.96~{\deg }^{2}.}