Q:

How often do lunar eclipses occur?

A:

Lunar eclipses occur two to four times each year. Lunar eclipses only occur during full moons, but because the orbit of the moon is tipped five degrees relative to Earth's orbit around the sun, not every full moon results in an eclipse. When an eclipse does occur, it's visible to everyone on Earth's night side.

There are three types of lunar eclipses. The moon's position relative to the umbra, which is the dark center of an eclipse shadow, determines which type is visible.

About 35 percent of lunar eclipses are total eclipses, and they are the best-known and most-watched type. Although direct sunlight is completely blocked by Earth, indirect light still reaches the moon's surface. The earth's shadow filters out blue-colored light, giving the moon a spectacular rust-colored hue.

A partial lunar eclipse occurs when only part of the moon passes through Earth's shadow. Partial eclipses make up about 30 percent of all lunar eclipses, and they are visible to the naked eye.

Penumbral lunar eclipses, which make up about 35 percent of lunar eclipses, occur when the moon passes through the earth's penumbra, which is the partial shadow that is visible around the umbra's periphery. This type of eclipse is difficult to see with the naked eye, and usually is of interest only to astronomers.

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