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The Cause of the Moon's Shape Changes

Started by curtrenz, 10/13/2007 07:36AM
Posted 10/13/2007 07:36AM Opening Post
Here’s a diagram I’ve created for those who need to understand the cause of the different phases of the Moon, or have the mistaken belief that the dark portion of the Moon’s face is due to the Earth’s shadow. That is only true during a lunar eclipse. Normally the dark portion is actually on the night side of the Moon, which is out of sight of the Sun. It is daytime for the light portion, which is receiving direct sunlight.

Imagine you are viewing the diagram from outer space well above the Earth’s arctic region. The Sun is far away in the direction of the arrows. The Moon is moving counterclockwise in its nearly circular orbit, which is colored orange in the diagram. After an average of 29.53 days the Moon is back to its original relationship with the Earth and Sun.

The images in the inner ring show how the Moon appears to a person standing on Earth when looking at the Moon in that direction. The sizes of the images in the diagram are not to actual scale. wink

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Curt Renz
Posted 10/14/2007 06:11AM #1

I teach physical and environmental sciences and I am going to use your diagram when explaining the moon's phases to my students, if that is okay with you.

Thanks and clear skies.

Tom B.