From Earth, the Moon looks like a round disk in the sky. At times this disk appears to have part of it cut away or is overlapped by something that is dark.
The edge or line where the lighted part of the moon disk ends is called the terminator. In the Northern Hemisphere, the terminator always appears to move toward the east (to the left when viewing the disk).
Using this information, for the Moons in the diagram: that:
Moon A is waning, which means the lighted part is getting smaller.
Moon B is waxing, which means the lighted part is getting smaller.
The Lunar Cycle Challenge example shows a sequence of waxing moon phases with one of the phases missing. The best choice is moon phase C, which would fit show more lighted area than box 1 and less lighted area than box 3.
To test your skills at predicting lunar phases, click
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