Which of the following best explains why the Moon has phases as seen from Earth?

• A. The Moon's phases are due to clouds on Earth blocking parts of the Moon at different times.
• B. The Moon's phases occur because the Moon emits its own light, which changes in intensity over time.
• C. The Moon's phases are caused by its position relative to the Earth and Sun, resulting in varying portions of its illuminated half being visible from Earth.
• D. The Moon's phases result from the Earth's shadow falling on the Moon during its orbit.

Answer: (C)

Verified step by step guidance

1. Understand that the Moon does not produce its own light; instead, it reflects sunlight. This means the brightness we see depends on how much of the Moon's sunlit side is visible from Earth.
2. Recognize that the Moon orbits the Earth, and as it moves, the angle between the Earth, Moon, and Sun changes. This changing angle affects how much of the illuminated half of the Moon we can see.
3. Recall that the phases of the Moon are the different shapes of the sunlit portion visible from Earth, ranging from new moon (no visible light) to full moon (fully illuminated).
4. Eliminate incorrect explanations: clouds blocking the Moon would cause temporary obscuration, not phases; the Moon does not emit light; Earth's shadow causes lunar eclipses, which are rare and not the cause of regular phases.
5. Conclude that the best explanation is that the Moon's phases result from its position relative to the Earth and Sun, which changes the visible portion of its illuminated half.