For the first time in 99 years, a solar eclipse tracked across the entire continental United States. On 21 August, millions of people watched this spectacular celestial event. A solar eclipse occurs when the moon passes between Earth and the Sun, obscuring the Sun from view. Viewers along the ’path of totality’, which stretched from northwest Oregon to South Carolina, witnessed the moon completely covering the Sun. Solar eclipses usually occur less than once a year, and can only be seen from a small area of the Earth's surface. View images from this year’s and past eclipses.