What phase of the moon leads to a lunar eclipse?

A lunar eclipse occurs when the Earth is positioned directly between the Sun and the Moon, causing the Earth's shadow to fall on the Moon. This alignment only happens during the full moon phase, when the Moon is on the opposite side of the Earth from the Sun. During this phase, the Moon is fully illuminated by sunlight, making it more susceptible to being shadowed by the Earth, leading to the visual phenomenon of a lunar eclipse. The other phases do not provide the necessary alignment for an eclipse because at those times, the Sun, Earth, and Moon are not in a straight line.