Correct Response: C. Lunar eclipses occur when the Moon moves across the Sun, producing a shadow on Earth. A lunar eclipse can only occur when the Moon is in a direct line between the Sun and Earth. Since the Moon's orbit of Earth is tilted 5 degrees relative to Earth's orbital plane (the ecliptic), this lineup can only occur two or three times a year and not each time the Moon completes its orbit of Earth. Neither Earth's axial tilt relative to the plane of its orbit (A) nor the different orbital periods of Earth and the Moon (B) affect the relationship between Earth, the Moon, and the Sun that produces lunar eclipses. The Moon's orbital period (27 days) is much longer than Earth's 24-hour rotational period (D), but that difference is also not responsible for the rarity of lunar eclipses each year.
