Which phase is the Moon shown as a half-illuminated disk with the left side lit?

Which phase is the Moon shown as a half-illuminated disk with the left side lit?

• A. First Quarter
• B. New Moon
• C. Full Moon
• D. Third Quarter

Answer: (D)

Half of the Moon’s disk being illuminated indicates a quarter Moon. The side that glows shows whether it’s waxing or waning: the right half lit means waxing toward the first quarter, while the left half lit means waning toward the New Moon. So when the left side is illuminated, you’re observing the last quarter (also called the third quarter) phase. New Moon would be nearly invisible, and a Full Moon would have the entire disk lit.

Half of the Moon’s disk being illuminated indicates a quarter Moon. The side that glows shows whether it’s waxing or waning: the right half lit means waxing toward the first quarter, while the left half lit means waning toward the New Moon. So when the left side is illuminated, you’re observing the last quarter (also called the third quarter) phase. New Moon would be nearly invisible, and a Full Moon would have the entire disk lit.