Throughout history, eclipses have triggered awe and sometimes fear, as people didn't know what caused these apparently otherworldly changes in the sky. A lunar eclipse occurs during full moon when the Earth perfectly blocks the sun's light from illuminating the moon because the sun, Earth and moon are perfectly lined up in a straight-line, "syzygy" configuration. When the moon passes through the Earth's umbral shadow, it's a total lunar eclipse. Sometimes, the moon passes through the penumbra (the part of the Earth's shadow that isn't totally dark) for a penumbral eclipse, but total penumbral eclipses are rare. During a partial lunar eclipse, just a portion of the moon passes through Earth's umbral shadow.