Ben decides to help an arachnachimp on his lunar quest for a crystal.Ben decides to help an arachnachimp on his lunar quest for a crystal.Ben decides to help an arachnachimp on his lunar quest for a crystal.
When the team visits the moon, it's a full moon. When they're on the moon, it's a full Earth in the moon's sky. The sun can't be fully illuminating both. At least one must be in shadow (presumably Earth).