Crescent SunThe moon appears to take a bite out of the sun over Manila in the Philippines during a partial solar eclipse in January 2009. Tomorrow sky-watchers in parts of Europe and Africa will be treated to a similar sight during the first of four partial solar eclipses slated to happen in 2011.Solar eclipses occur when Earth, the moon, and the sun are aligned so that—as seen from Earth—the moon appears to cover all or part of the sun's disk, and Earth is cast in shadow. Partial solar eclipses happen when Earth crosses only through the faint outer part of the moon's shadow, known as the penumbra.On Tuesday the moon's silhouette will start to move across the sun at 6:40 a.m. UT, when the penumbra hits Algeria. The last traces of the moon's outer shadow will cross northwest China at 11 a.m. UT.Find out more about tomorrow's solar eclipse >>

With reporting by Andrew Fazekas

Photograph by Aaron Favila, AP