On Wednesday, the moon will pass between Earth and the sun, casting its shadow across two continents in one of nature's most humbling demonstrations of celestial order. Total darkness will fall briefly over Iceland, Greenland, Russia, Spain, and Portugal — places where day will become twilight and stars will appear at noon — while millions across the northern United States will witness a partial dimming of the sun's face. Spain, which has not experienced totality from its mainland since 1905, will have two minutes to remember. For those in the path of the shadow, and for the scientists who wil