Square degree
Encyclopedia : S : SQ : SQU : Square degree
A square degree is a non-SI unit that can be used to measure solid angles (that is, the area of the projection of a surface onto a unit sphere centered on the point of observation). It is the two-dimensional equivalent of the degree and may be denoted "sq.deg.", "deg²", or a symbol of a square followed by °.
The number of square degrees in the whole sky is 129,600/π (that is, approximately 41,253 sq.deg.) which can be derived from that the fact that the whole sky covers 4π steradians, and one degree is π/180 radians. Thus, one square degree is approximately 1/3283 steradian or 305 microsteradians.
For example, observed from the surface of the Earth, the Moon has a diameter of approximately ½º, so it covers an area of approximately 0.2 sq.deg.
External link
From Wikipedia, the Free Encyclopedia. Original article here. Support Wikipedia by contributing or donating.
All text is available under the terms of the GNU Free Documentation License See Wikipedia Copyrights for details.