Question

first quarter

• the moon is one quarter of the way through its cycle
• from earth, it appears to be half lit on the right

which side of the moon is illuminated during the first quarter?

Explanation:

The text explicitly states that during the first quarter, from Earth, the Moon appears half lit on the right. This directly answers which side is illuminated.

Answer:

The right side of the Moon is illuminated during the first quarter.