Why does the moon appear to change shape throughout each month? aThe fraction of the moon that is lit by the sun changes. bDifferent parts of the moon become visible from Earth as the moon rotates. cDifferent parts of the sunlit area are visible from Earth due to motions in the Earth-sun-moon system.

The moon appears to change shape throughout each month due to a combination of factors:

a) The fraction of the moon that is lit by the sun changes: This is due to the moon's orbit around the Earth. As the moon orbits the Earth, different parts of it are illuminated by the sun, causing the visible portion of the moon to change.

b) Different parts of the moon become visible from Earth as the moon rotates: The moon rotates on its axis at the same rate that it orbits the Earth. This means that we always see the same side of the moon from Earth. However, as the moon orbits the Earth, different parts of the moon's surface are illuminated by the sun, causing the visible shape of the moon to change.

c) Different parts of the sunlit area are visible from Earth due to motions in the Earth-sun-moon system: The Earth also orbits the sun, and the moon orbits the Earth. This means that the relative positions of the Earth, sun, and moon are constantly changing. As a result, the part of the moon that is illuminated by the sun (and therefore visible from Earth) changes over time.

In summary, the moon appears to change shape throughout each month due to the changing illumination of the moon by the sun, the rotation of the moon, and the relative motions of the Earth, sun, and moon.