Sentence:  The variation in the 3 - cm emission of the moon during a lunation is very much less than the variation in the 8.6 - mm emission , as would be expected from the <WSD>explanation</WSD> of Piddington and Minnett ( 1949 ) . 
Meaning of the word marked with <WSD> tags:  a statement that makes something comprehensible by describing the relevant structure or operation or circumstances etc.