Sentence:  The ratio of the measured antenna temperature change during a drift scan across the moon to the average brightness temperature of the moon over the antenna beam ( assuming that the brightness <WSD>temperature</WSD> of the sky is negligible ) was found , by graphical integration of the antenna directivity diagram , to be 0.85 . 
Meaning of the word marked with <WSD> tags:  the degree of hotness or coldness of a body or environment (corresponding to its molecular activity)