Square degree
unit of solid angle; (π/180)² steradians
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}.}
Subdivisions
Each square degree is equal to 3600 square arcminutes, and each square arcminute is equal to 3600 square arcseconds. So, each square degree is equal to 12960000 square arcseconds. The whole sphere contains about 148.51 million square arcminutes and about 534.64 billion square arcseconds.
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This entry incorporates text from “Square degree” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.