Question

Why do we see different phases of the lunar cycle?

As the moon rotates around its axis, different sides of it become visible.
As Earth rotates around its axis, people can see different sides of the moon.
As Earth revolves around the Sun, the moon is cast in different shadows by Earth.
As the moon revolves around Earth, the different amounts of the sunlit side faces Earth.

Answer 1

Correct answer: As the moon revolves around Earth, the different amounts of the sunlit side faces Earth.

Why: Half of the Moon is always lit by the Sun. As the Moon orbits Earth, the angle between the Sun, Moon and Earth changes, so we see more or less of the illuminated half — producing the phases (new, crescent, quarter, gibbous, full, etc.).

Why the other choices are wrong:
- The Moon does rotate on its axis, but it is tidally locked to Earth so the same face points toward us; its rotation does not make different sides visible.
- Earth’s daily rotation only changes when the Moon rises and sets for an observer; it doesn’t change which part of the Moon is lit.
- Earth’s shadow causes lunar eclipses only when the Sun, Earth and Moon are specially aligned (rarely), not the regular monthly phases.