Which phase occurs when the Moon is mostly illuminated but decreasing?

Which phase occurs when the Moon is mostly illuminated but decreasing?

• A. Waning Gibbous
• B. Waxing Crescent
• C. New Moon
• D. Third Quarter

Answer: (A)

Moon phases reflect both how much of the Moon’s surface is lit and whether that lit portion is growing or shrinking. When the illuminated part is more than half but the amount of light is decreasing, that phase is Waning Gibbous. It occurs after a Full Moon as the Moon moves toward New Moon, so you still see most of the face lit, but the brightness is getting smaller each day. The other options don’t fit: Waxing Crescent is less than half and increasing, New Moon is barely lit, and Third Quarter is exactly half lit and decreasing, not “mostly illuminated.”

Moon phases reflect both how much of the Moon’s surface is lit and whether that lit portion is growing or shrinking. When the illuminated part is more than half but the amount of light is decreasing, that phase is Waning Gibbous. It occurs after a Full Moon as the Moon moves toward New Moon, so you still see most of the face lit, but the brightness is getting smaller each day. The other options don’t fit: Waxing Crescent is less than half and increasing, New Moon is barely lit, and Third Quarter is exactly half lit and decreasing, not “mostly illuminated.”