Why do we observe the Moon in different phases over a month?

• A. Because of the Moon's orbit around Earth and the varying sunlit portion we see
• B. Because of Earth's rotation
• C. Because of weather
• D. Because of the Sun's changing brightness

Answer: (A)

The Moon’s appearance changes because it orbits Earth and the Sun lights only part of it. The Sun’s light always shines on the Moon, but as the Moon moves around Earth, the angle between the Sun, Moon, and Earth changes. That means we see different fractions of the Moon’s lit side from Earth over time. When the Moon is between the Sun and Earth, we see little to no lit face (new Moon). As it moves, more of the lit side becomes visible, giving crescent, quarter, and gibbous phases, until a full Moon when the entire face facing us is lit. Then the cycle repeats roughly every month. It’s not about weather, Earth’s rotation, or the Sun changing brightness—the changing geometry is what creates the Moon’s changing appearances.