Final answer:
When the illuminated part of the moon gets smaller each night, the moon is in its waning phases. This happens after the full moon and continues until the new moon.
Step-by-step explanation:
When the illuminated part of the moon appears to become smaller from night to night, its phases are said to be waning. The waning phases occur after the full moon, when the moon moves from full to new, and its visible illuminated area decreases each night. This process is the opposite of waxing when the moon's illumination grows.
The lunar cycle consists of several distinct phases, starting with the new moon, then waxing to the first quarter, waxing gibbous, full moon, waning gibbous, third (or last) quarter, and finally waning crescent before starting a new cycle. The moon's orbit around Earth and the corresponding angle of the sunlight hitting the moon dictate these phases.