The first quarter Moon is illuminated by about how much?

The first quarter Moon is illuminated by about how much?

• A. Half illuminated
• B. One-quarter illuminated
• C. Three-quarters illuminated
• D. Full illuminated

Answer: (A)

The visible fraction of the Moon’s sunlit side depends on the angle between the Sun, Moon, and Earth. At the first quarter, that angle is about 90 degrees, so roughly half of the portion we can see is illuminated. That’s why the first quarter appears half-lit. The other options don’t fit this phase: one-quarter illuminated would be much less than what you see, three-quarters would look more than half-lit, and full illuminated is what you see during a full Moon.

The visible fraction of the Moon’s sunlit side depends on the angle between the Sun, Moon, and Earth. At the first quarter, that angle is about 90 degrees, so roughly half of the portion we can see is illuminated. That’s why the first quarter appears half-lit. The other options don’t fit this phase: one-quarter illuminated would be much less than what you see, three-quarters would look more than half-lit, and full illuminated is what you see during a full Moon.