How Does the Terminator Appear to Move?
As viewed from the Northern Hemisphere, the full moon phase appears to be a white disk-shaped object in the night sky.
From one day to the next, the white disk changes shape as the white, lighted part decreases. The line separating the lighted and unlighted part of the disk is called the terminator.
Have Some Fun With the Moon
Step into Janice’s Fantasy World.
When the Moon is waning, it changes from a full moon (fully lite white disk) to a new moon (unlit disk). One could imagine that the hand is pulling the night sky over the lighted disk. In the Northern Hemisphere the terminator moves toward the left (eastward).
When the moon is waxing, the Moon changes from a new moon to a full moon. This time, the imaginary hand is pulling a blanket of light across the darkened disk.
Back to the Real World Of Science
The changes in the shape of the lighted part of the Moon disk facing Earth is due to the location of the Moon, Earth, and Sun. During full moon, the Moon lies on the opposite of the Earth from the Sun. During new moon, the Moon lies between the Earth and the Sun.