What Causes a Crescent Moon?

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Crescent moons happen when Earth, the sun and moon are positioned in a way that only shows a portion of the reflected light on the moon. The result is a crescent-shaped light pattern.

Moon phases are dictated by the moon’s position relative to the sun and Earth. One phase, the crescent moon, happens when the moon is positioned at an angle to Earth that shows only a small, crescent-shaped portion of the moon illuminated by the sun. Half of the moon always reflects sunlight. However, the visible amount of this reflection depends on the relative positions of Earth, the sun and moon. Because the moon’s position relative to the Earth changes daily, the amount of visible reflected light also changes, and that results in the moon phases.