Sentence:  And should the moon happen to hit its ever-shifting orbital perigee at the same time that it lies <WSD>athwart</WSD> from the sun, we are treated to a so-called supermoon, a full moon that can seem close enough to embrace – as much as 12 percent bigger and 30 percent brighter than the average full moon. 
Meaning of the word marked with <WSD> tags:  Across the path (of something).