Why do eclipses of the moon occur?

The earths cast a long shadow in to the slpace, away from the Sun. If the moon passes through this shadow, it grows dim. This can happen onl on ‘full moon, . When it is opposite the sun. However, since the moon’s orbit is tilted, it usually passes to one side of the shadow.
The earth shadow is not really black, since some sunlight filters reddish into it and the eclipse moon can last for over one and a half hours, if the moon passes through the shadow’s center. There is a faint outer shadow or ‘Penumbra’ around the central ‘umbra’.