Sentence:  ... I rubbed my eyes, doubting the very evidence of my own eyesight—"a" or "the" huge man in his shirt-sleeves; yes, positively not sunning but "mooning" himself—<WSD>apricating</WSD> himself in the occasional moonbeams; and, as if simple star-gazing from a sedentary station were not sufficient on such a night, absolutely pursuing his astrological studies, I repeat, in his shirt-sleeves! 
Meaning of the word marked with <WSD> tags:  To bask in the sun.