A lunar eclipse is an astronomical phenomenon. It happens when the moon passes through the shadow of the Earth. Lunar eclipses happen about twice a year, much more often than solar eclipses. They also last longer than solar eclipses.
During a lunar eclipse, the Moon looks red-brown. It may be thought that the Moon is completely black because of the Earth's shadow, but the reddish-brown color is because of the fact that the Sun's light reflects off of the Earth, and is barely visible on the Moon.
Like solar eclipses, there are different types of lunar eclipses. There are total eclipses, where all of the moon appears reddish-brown, and partial ones, where only part of the moon appears reddish-brown.
Lunar eclipses are not as rare as solar eclipses and are sometimes called the "Yellow Moon" although it does not look very yellow.