Which phenomenon is primarily caused by the Moon's movement around the Earth?

• A. Eclipses
• B. Phases
• C. Orbits
• D. Tides

Answer: (B)

The changing appearance of the Moon in our sky is driven by its position as it orbits Earth. As the Moon moves around us, the Sun lights different portions of its near side, and from Earth we see a varying fraction of the illuminated half. That’s why we cycle through the phases—from new moon to crescent, first quarter, gibbous, and full moon—and this pattern repeats about every 29.5 days.

Eclipses happen only when the Sun, Moon, and Earth align in just the right way, which is a special case and not what you observe most days. Tides come from the Moon’s gravity pulling on Earth's oceans, another effect that depends on distance and alignment but isn’t the everyday change we call the Moon’s phases.