What astronomical event can only occur during a full moon?

A lunar eclipse is the only astronomical event among the choices that can occur only during a full moon. During a lunar eclipse, the Earth comes directly between the sun and the moon, casting a shadow on the moon. This alignment can only happen when the moon is fully illuminated, which is characteristic of the full moon phase.

In contrast, a solar eclipse occurs when the moon passes between the Earth and the sun, which can only happen during a new moon. Planetary alignments are not restricted to any specific phase of the moon and can occur at various times when planets align in the sky. Meteor showers are also not dependent on the moon’s phase; they happen periodically throughout the year regardless of whether the moon is full or not. Thus, the occurrence of a lunar eclipse is uniquely tied to the full moon's position in relation to the Earth and the sun.