Which of these (hypothetical) modiﬁcations would cause lunar eclipses to happen once per month?
A) Make the Moon orbit the Earth twice as fast.
B) Relocate the Moon to twice its current distance from the Earth.
C) Change the Moon's orbital plane so it tilts the opposite way.
D) Change the orbital plane of the Moon so it lies in the same plane as Earth's orbit around the Sun.

Question

Quizplus · Accepted Answer

A lunar eclipse occurs when the Earth passes between the Sun and the Moon, casting a shadow on the Moon. For a lunar eclipse to occur once per month, the Moon must pass through the Earth's shadow every month. This can only happen if the Moon's orbital plane is in the same plane as the Earth's orbit around the Sun, so that the Earth's shadow falls on the Moon during each orbit. Therefore, changing the Moon's orbital plane to lie in the same plane as Earth's orbit around the Sun would cause lunar eclipses to happen once per month. The other three options would not have this effect.

Which of These (Hypothetical) Modiﬁcations Would Cause Lunar Eclipses to Happen