When does a full moon occur?

A full moon occurs when the Moon is positioned on the opposite side of Earth from the Sun. This alignment allows the entire illuminated portion of the Moon to be visible from Earth, making it appear fully lit in the night sky. During this phase, the Earth is situated directly between the Sun and the Moon, receiving sunlight on the side of the Moon that faces Earth.

This phenomenon is essential in understanding lunar cycles and tides, as the gravitational interactions during a full moon can significantly influence ocean tides. The brightness and visibility of the full moon also contribute to various cultural and natural events, marking significant moments in calendars and folklore.

In the context of the other options, the position of the Moon between the Earth and the Sun indicates a new moon, while being farthest from the Sun (aphelion) does not have a direct correlation with the phase of the Moon. Finally, the Moon traveling through Earth's shadow describes a lunar eclipse, not a full moon.