An eclipse of the moon occurs when the Earth comes between the sun and the moon.
During a lunar eclipse, the Earth blocks the sun's light from reaching the moon, causing the moon to appear darkened or reddish in color. This occurs because the Earth casts its shadow onto the moon, which is why it is also called a "shadow play".
A lunar eclipse can only occur during a full moon phase, when the sun, Earth, and moon are aligned in a straight line. However, it does not occur during every full moon because the moon's orbit is tilted relative to the Earth's orbit around the sun.
In contrast, a solar eclipse occurs when the moon passes between the sun and the Earth, blocking the sun's light from reaching parts of the Earth.
Overall, the occurrence of a lunar eclipse is a result of the relative positions and movements of the Earth, moon, and sun in space.