Sentence:  <WSD>Mars</WSD> has been observed twice at about 3 - cm wave length , and the intensity of the observed radiation is in reasonable agreement with the thermal radiation which might be predicted on the basis of the known temperature of Mars . 
Meaning of the word marked with <WSD> tags:  a small reddish planet that is the 4th from the sun and is periodically visible to the naked eye; minerals rich in iron cover its surface and are responsible for its characteristic color