Is the full moon ten times brighter than the half moon?


Dear Tom,

I have read that the full moon is ten times brighter than the half moon. Can this be possible?

Elizabeth Cummings,

Dear Elizabeth,

It is true. The Earth’s moon possesses a rocky surface that shines by reflected light. Its face is so deeply scarred that, as viewed from the Earth, much of its surface is in shadow.

Light reflected back to our eyes is maximized when sunlight shines down of the center of the moon’s face, the only portion that “looks” straight at us. But during a half moon we are viewing only a poorly illuminated periphery of the face.

Our view of the center of the moon’s face is best during a full moon, when the moon is in a position in its orbit that the sun is behind us and the moon is in the opposite side of the sky. That is when sunlight best illuminates the moon’s deepest features and reduces its shadows.


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