Sky-watchers across the United States are gearing up for the best cosmic spectacle in nearly a century, when a total solar eclipse will race over the entire country for the first time since 1918. On August 21, tens of millions of lucky people will be able to watch the moon completely cover the sun and turn day into night for a few fleeting minutes.

The main event will be visible from a relatively narrow path, starting in Oregon and ending in South Carolina. In between, the total eclipse will cross multiple cities in 12 states, prompting plans for countless watch parties, cosmic-themed tours, and scientific observations. (Also see "100 Years of Eclipse-Chasing Revealed in Quirky Pictures.")

While many people