During the first and third quarters, which statement is true about the Moon's illumination?

During the first and third quarters, which statement is true about the Moon's illumination?

• A. The Moon is fully illuminated.
• B. The Moon is not illuminated.
• C. The Moon is half illuminated.
• D. The Moon is quarter illuminated.

Answer: (D)

Moon illumination depends on how much of the Sunlit side of the Moon we can see from Earth. During the first and third quarter phases, the Sun, Moon, and Earth form a right angle, so sunlight hits exactly half of the Moon’s near side. We see a half-moon, meaning about 50% of the Moon is illuminated. In everyday terms this is often described as a quarter moon, since it’s one of the four main phases, but the key point is the illuminated fraction is half. The full moon has all of the near side lit, and the new moon has none, so those describe the other points in the cycle.

Moon illumination depends on how much of the Sunlit side of the Moon we can see from Earth. During the first and third quarter phases, the Sun, Moon, and Earth form a right angle, so sunlight hits exactly half of the Moon’s near side. We see a half-moon, meaning about 50% of the Moon is illuminated. In everyday terms this is often described as a quarter moon, since it’s one of the four main phases, but the key point is the illuminated fraction is half. The full moon has all of the near side lit, and the new moon has none, so those describe the other points in the cycle.