A celestial dragon will chew on the Moon Thursday evening and Friday morning, drenching the normally predictable satellite in blood-red hues before finally consuming it entirely from our night sky.

That's how the ancient Chinese explained lunar eclipses. The events terrified many cultures through time. But now scientists can explain the mechanics of an eclipse and predict its timing and duration, and there is nothing to be frightened about.

But what exactly is behind a total eclipse of the Moon? And why do they occur on a seemingly erratic schedule? How long do they last?

Here are 10 facts that will both illuminate the dark history of lunar eclipses and give you some science to chew on as you gaze up and watch Earth's satellite disappear May 15-16, in the first total lunar eclipse in three years for most of the Western Hemisphere.

The cause of lunar eclipses is simple: Earth gets in the way.

The Moon is a visible beacon because it reflects sunlight. The Moon makes no light of its own. Earth always casts a shadow into space, and every now and then everything aligns just right so that the shadow falls on the Moon.

Lunar eclipses can only occur at full Moon, that time each month when the Moon is directly opposite the Earth in relation to the Sun. [See a graphic]

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