Square degree

A square degree is a non-SI unit measure of solid angle. It is denoted in various ways, including deg², 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 or about 1/3283 steradian. The number of square degrees in a whole sphere is

$4\pi \left({\frac {180}{\pi }}\right)^{2}={\frac {129\,600}{\pi }},$

or approximately 41,253 deg². This is the total area of the 88 constellations in the list of constellations by area.

For example, observed from the surface of the Earth, the Moon has a diameter of approximately 0.5°, so it covers a solid angle of approximately 0.196 deg², which is 4.8 × 10⁻⁶ of the total sky sphere.

External links

• http://calgary.rasc.ca/constellation.htm#square