What phase of the moon can be seen when it is fully illuminated?

• A. New moon
• B. Waxing gibbous
• C. First quarter
• D. Full moon

Answer: (D)

The phase of the moon that is fully illuminated is known as the full moon. During this phase, the entire side of the moon that faces Earth is reflecting sunlight, making it appear bright and round in the night sky. This happens when the Earth is between the sun and the moon, allowing for maximum illumination.

In contrast, other phases like the new moon occur when the moon is positioned between the Earth and the sun, making it virtually invisible from our perspective. Similarly, the waxing gibbous phase indicates that more than half of the moon's surface is illuminated but not completely, and the first quarter phase shows half of the moon illuminated, but not fully. Therefore, the full moon is unique for being the point at which the moon’s surface is entirely lit up by the sun.