Sentence:  The antenna patterns and the power gain at the peak of the beam were both measured ( Mayer , McCullough , and Sloanaker , 1958 b ) , so that the absolute power sensitivity of the antenna beam over the <WSD>solid</WSD> angle of the moon was known . 
Meaning of the word marked with <WSD> tags:  an angle formed by three or more planes intersecting at a common point (the vertex)