Every now and then, the Sun, Earth, and Moon align so that, when viewed from the Earth, the Moon eclipses the Sun's light. Solar eclipses are fairly common -- the Moon will block out some portion of the Sun at least twice a year. However, it is still a special event to be able to witness a total solar eclipse. In this video segment adapted from NASA, learn how solar eclipses happen and why they are so difficult to witness.
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