Solid angle on the celestial sphere

Solid Angle

The concept of solid angle Q is fundamental to all of astronomy. It is simply an angular area on the sky, or equivalently, on the celestial sphere. This area can be expressed as square degrees or square radians the latter unit is called the The solid angle is expressed in terms of two angular displacements, e.g., d9 and d0 in Fig. 7. The beam of an antenna, e.g., 1 x 1 , or 1x 2, or a fan beam of 1 x 100 can be characterized by its solid angle, approximately 1 deg2, 2 arcsec2, and 100 deg2 for...