What phenomenon occurs when the Earth lies between the Moon and the Sun?

The correct choice is a lunar eclipse, which occurs when the Earth is positioned directly between the Moon and the Sun. In this scenario, the Earth's shadow is cast on the Moon, leading to a temporary darkening of the Moon's surface. During a lunar eclipse, people on the night side of the Earth can observe this event, as the Earth completely blocks sunlight from reaching the Moon.

In contrast, the other options refer to different astronomical phenomena. A solar eclipse occurs when the Moon is between the Earth and the Sun, blocking sunlight from reaching the Earth. An equinox refers to the time of year when day and night are approximately equal in length, which is related to the tilt of the Earth's axis rather than the positions of the Earth, Moon, and Sun in a straight line. A full moon, while related to the lunar phase when the Moon is fully illuminated by sunlight, does not involve the Earth's shadow and is not an eclipse situation. Understanding these distinctions clarifies why a lunar eclipse is the phenomenon that occurs when the Earth is positioned between the Moon and the Sun.