What Is a Lunar Eclipse?

A solar eclipse occurs when the moon passes directly between the sun and the earth. When the earth passes directly between the moon and the sun, a lunar eclipse occurs.

A lunar eclipse can happen only when the moon is full, because then it is on the other side of the earth from the sun. The earth casts a long shadow through space.

As the full moon passes into this shadow, people on earth can see the edge of the earth's shadow as it passes across the moon. The curve of the earth's shadow as it passes across the moon was one of man's first signs that the earth is round.

In any year, there may be no lunar eclipses or as many as three. No lunar eclipse can last more than 104 minutes.