Solar Eclipse Definition
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A solar eclipse occurs when an observer (on Earth ) passes through the shadow cast by the Moon which fully or partially blocks (" occults ") the Sun . This can only happen when the Sun , Moon and Earth are nearly aligned on a straight line in three dimensions ( syzygy ) during a new moon when the Moon is close to the ecliptic plane .  In a total eclipse , the disk of the Sun is fully obscured by the Moon. In partial and annular eclipses , only part of the Sun is obscured.