It will be the first total solar eclipse to sweep coast-to-coast across the U.S. in 99 years.
With 200 million people within a day's drive of the path of totality, towns and parks are bracing for monumental crowds. It's expected to be the most observed, most studied and most photographed eclipse ever. Not to mention the most festive, what with all the parties.
Astronomers consider a full solar eclipse the grandest of cosmic spectacles. Southernmost Illinois will see the most darkness: 2 minutes and 44 seconds.
All of North America will get at least a partial eclipse.
