The moon appears to be getting smaller during week 3 and week 4 in its cycle.
During the moon's cycle, the moon appears to be getting smaller in week 3 and week 4.
The moon goes through a 4-week cycle, also known as a lunar cycle. During this cycle, the moon appears to change its shape in the sky. The moon appears to be getting smaller during weeks 3 and 4 of the lunar cycle. So, the answer to the question is "week 3 and week 4".