The Moon is spherical, and half of it is always illuminated (or lit) by the Sun. However, the amount of the illuminated half of the Moon that is visible to people on Earth is constantly changing.

Explore these two videos to visualize how half of the Moon is always illuminated by sunlight no matter what it looks like from Earth. Pay attention to where the Sun is located in each video and how sunlight shines on the Moon and Earth. An overhead, or space, view shows the Moon’s orbit as a circle.

Imagine what the system would look like if the Sun were always located on the left of the screen. As the video shifts from the space view to what the Moon looks like from Earth, you can see which part of the sunlit half of the Moon is facing Earth. For each video, consider how much of the Moon is illuminated by the Sun and how much of that illuminated part is visible from Earth.

Watch the videos, then answer the questions on Handout 2.