Answer: when the full moon moves through Earth’s shadow, which only happens when Earth is between the Moon and the Sun and all three are lined up in the same plane, called the ecliptic In an eclipse, Earth’s shadow has two distinct parts the umbra and the penumbra. The umbra is the inner, cone-shaped part of the shadow, in which all of the light has been blocked. The penumbra is the outer part of Earth’s shadow where only part of the light is blocked. In the penumbra, the light is dimmed but not totally absent.
