Americans with telescopes, cameras and protective glasses are staking out viewing spots to watch the moon blot out the midday sun Monday.

It promises to be the most observed and photographed eclipse in history. The main drag will stretch along a narrow corridor from Oregon to South Carolina. Millions of eclipse watchers are expected to peer skyward, and they're hoping for clear weather.

It will be the first total solar eclipse to sweep coast-to-coast across the U.S. in 99 years.