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The following diagram shows various positions of the moon in its orbit around Earth. The image of the moon shows its phase as seen from Earth.

Earth is shown with a bigger circle on the right is a bigger circle labeled as Sun. Two lunar phases are shown. First quarter is shown above Earth and the Third Quarter below Earth. Arrows are drawn in the counter clockwise direction. Position A is marked on the left of Earth, position B is marked halfway between position A and the Third Quarter. Position C is marked on the right of Earth, position D is marked halfway between position C and the First Quarter.

Considering the position of the Sun in the diagram, in which position will three-fourths of the moon's illuminated side be visible from Earth?

A
B
C
D

1 answer

To determine the position from which three-fourths of the moon's illuminated side is visible from Earth, we need to understand the moon phases relative to the positions indicated in the diagram.

  • Position A: The moon is positioned (to the left of Earth) where it is a New Moon (not illuminated from Earth's perspective). Therefore, none of the illuminated side would be visible.
  • Position B: This position is halfway between A (New Moon) and the Third Quarter. Here, the moon would be in a Waxing Crescent phase, which means less than one-half is illuminated; therefore, not three-fourths.
  • Position C: This position is to the right of Earth, where it would be a Full Moon. Here, the entire illuminated side (100%) is visible, not three-fourths.
  • Position D: This position is halfway between the Full Moon (Position C) and the First Quarter. This location represents a Waxing Gibbous phase, where greater than one-half and up to three-fourths of the moon’s illuminated side is visible.

So, the correct answer for the position where three-fourths of the moon's illuminated side will be visible from Earth is:

D.