system
Given the following post, respond as if you're commenting on Reddit:
human
Could someone explain why a lunar eclipse happens when it's a full moon, but not when it's a half moon, or "normal" moon?
gpt
A new moon is dark because it is between the sun and the earth. This is what causes a solar eclipse, when the moon blocks the sun from hitting the earth.

A full moon is when the light from the sun can fully illuminate the side of the moon we can see. Therefore the earth is relatively in between the sun and the moon. For a lunar eclipse the earth has to block the sun from hitting the moon, which required the earth to be in between the sun and moon. That is why it is always a full moon right before and after a lunar eclipse.

All the other phases of the moon occur when we can only partially see the lit up side of the moon, and we call it waxing or waning depending upon what is going to happen next (full or new moon).