Why are there Moon "phases"?

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            Click or tap on the Moon to move the "terminator"...

This is a model of the view from space. The relative sizes and distances are not in proportion to reality, nor is the tilt of the Moon's orbital plane when shown in the oblique view.

Explore just how much of the Moon is always in darkness -- for each position of the Moon in its orbit (shown by the light gray circle), click (or tap) on the Moon to move the terminator (the line between the illuminated part and dark part) until you think it is in the correct position. Then click "Check My Answer" button

You can change the view point at any time by clicking on the "Show Oblique View" (or "Show Top View") button.

When you click "Check My Answer", if you get it right you will be encouraged to move the Moon to a different position in its orbit, or, you will be instructed to try again to position the terminator correctly.

Upon demonstrating several first attempt correct answers you'll advance to another level to explore the view of the Moon as seen from Earth.

(In the initial views, the Earth is shown in the approximate position during Winter, with the Northern Hemisphere tilted toward the Sun.)

This applet is Copyright © 2012 by Tom Whittaker.
Images courtsey of NASA.