As you know, the moon is visible to us because its surface reflects the sun’s light. The moon takes close to four weeks to rotate once on its axis and the same time to orbit the Earth; therefore, we always see the same side. If we could see the Moon–Earth system from space, we would see that the side of the moon facing the sun is always the lit side, whereas the other side is always in the dark. As the moon orbits the Earth, the lit side that we see changes in size. These changes are called the lunar phases.
Which term describes the phenomenon where the moon appears to change its shape as seen from Earth over the course of a month?
a. Moon rotation
b. Lunar orbit
c. Lunar eclipse
d. Lunar phases