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__NOTOC__ A square degree (deg2) is a non SI-compliant 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, or about 1 / or 3.0462 steradian (0.30462 msr). The number of square degrees in a whole sphere is approximately deg2. This is the total area of the 88 modern constellations in the sky. : == Examples == * A whole sphere has deg2 * The full moon covers only about 0.2 deg2 of the sky when viewed from the surface of the Earth. The Moon is only a half degree across (i.e. a circular diameter of roughly 0.5 deg), so the moon's disk covers a circular area of: π ()2, or 0.2 square degrees. * Viewed from Earth, the Sun is roughly half a degree across (the same as the full moon) and covers only 0.2 deg2 as well. * It would take about times the full moon (or the Sun) to cover the entire celestial sphere. * Assuming the Earth to be a sphere with a surface area of 510 million km2, the area of Northern Ireland ( km2) and Connecticut ( km2) represent a solid angle of 1.1 deg2 and 1.2 deg2, respectively. * The largest constellation, Hydra, covers a solid angle of deg2, whereas the smallest, Crux, covers only 68 deg2.〔(RASC Calgary Centre - The Constellations )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Square degree」の詳細全文を読む スポンサード リンク
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