(1) A unit of measure of solid angle corresponding to the area, on a sphere of unit radius, of a quadrangle composed of great arcs 1^o. on a side. There are 129 600/π (approximately 41 250. 87) square degrees on a sphere, and approximately 3 282. 64 square degrees in a steradian. (2) A unit of area equal to 1/64 800 of the surface of a unit sphere. This definition and the preceding one do not define the same quantity. A solid angle (figure) having a solid angle (measure) of 1 square degree is not necessarily square. The quadrangle used in the first definition is not rectangular - the internal angles are slightly greater than 90^o and the sides bow out.