A total solar eclipse swept across parts of the Northern Hemisphere Wednesday, giving millions of skywatchers in the path of totality a chance to witness one of the year's biggest celestial events. A solar eclipse occurs when the moon passes between the Earth and the sun, casting a shadow on Earth that fully or partially blocks the sun, according to NASA. The view of the eclipse varies depending on location, with only those within the path of totality able to see the sun completely blocked by the moon. More this evening on #WorldNewsTonight.