Final answer:
A total lunar eclipse occurs when the Moon passes through Earth's shadow, also known as the umbra.
Step-by-step explanation:
A total lunar eclipse occurs when the Moon passes through Earth's shadow. The Earth's shadow, also known as the umbra, is the region where the Sun's light is completely blocked by Earth. During a total lunar eclipse, the Moon appears dark and may take on a reddish hue due to the Earth's atmosphere bending some sunlight into the umbra, causing it to reach the Moon.