Eclipses, once revered or feared, have now become a mass spectacle. At 1:51 p.m.

local time (seven hours more in mainland Spain), the Moon has completely covered the Sun, bringing with it a moment of disconcerting darkness. “It's an incredible thing, darkness at noon,” said Miles Blanton, a physics professor at the University of Arkansas. The weather report was the great concern of eclipse hunters in the United States this Monday, as clouds threatened to ruin the show.