The Physics of a "Blood Moon"

Once in a rare while, the moon turns red--because the sky is blue. That might sound like nonsense, but it's the simplest accurate way to explain what happened early this morning, when the moon disappeared from view before returning with an eerie, rusty cast to it. An image of the "Blue Blood Supermoon" taken over Kobe, Japan last night--the phenomenon attracted lots of attention, for being a coincidence of three lunar phenomena: a supermoon (where the moon is full at perigee), a lunar eclipse, a...