* The lunar cycle is continuous: The moon phases are a continuous cycle, so there isn't a single point directly opposite a full moon.
* New Moon is the closest: The closest phase to the "opposite" of a full moon is the new moon. This is when the moon is between the sun and the earth, and we can't see it.
Think of it this way:
* Full Moon: The moon is fully illuminated by the sun, and we see the entire face.
* New Moon: The moon is positioned so its dark side faces us.
The phases between these two points (waxing crescent, first quarter, waxing gibbous, waning gibbous, last quarter, waning crescent) are simply different stages in the lunar cycle.
