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
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.
Famous quotes containing the words square and/or degree:
“Interpreting the dance: young women in white dancing in a ring can only be virgins; old women in black dancing in a ring can only be witches; but middle-aged women in colors, square dancing...?”
—Mason Cooley (b. 1927)
“As to the bride, she is blithe as the month; if one can compare in any degree a weed of December, with the fragrance of May; for a weed in truth it is, and a weed not in its first prime.”
—Frances Burney (1752–1840)