Transcript: A Lunar eclipse occurs when the Earth passes between the Moon and the Sun, and the Earth casts a shadow on the Moon.  Lunar Eclipses are much more common than Solar eclipses because the Earth's shadow is much larger than the Moon's shadow, and the probability depends on the size of the shadow.  Neither Solar nor Lunar eclipses occur every month because the Moon's orbit of the Earth is tilted five degrees with respect to the Earth's orbit of the Sun.  So there are only two times in the year, the so-called "nodes," when eclipses can occur.  If you have ever seen a Lunar eclipse, you will notice that the Moon does not become entirely dark despite being in the Earth's shadow.  That's because light can refract through the Earth's atmosphere around the Earth leaving some dim illumination on the Moon itself.