Photos of the Nov. 8 Eclipse are here.

The second chance to see a total lunar eclipse in 2003 comes this weekend for most residents of North America and Europe. Two more in 2004 will round out this current spate of lunar disappearances. Then there will be a nearly 3-year drought.

What's going on? What causes an eclipse, and why do they occur on an irregular schedule?

Unpredictability is at the heart of eclipse lore. For the ancients, a lunar eclipse was a haunting event. Some believed a dragon of the sky was eating the Moon, flooding it with blood before consuming it entirely. Of course it always came back, and that fueled more speculation.

Here are 10 cool facts about the dark history of lunar eclipses and how they really work.

1) Earth gets in the way

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. It's like you, representing the Earth, standing in front of a bright light and casting a shadow on a child. [See a graphic]

This week's total lunar eclipse occurs Saturday evening, Nov. 8 in North and South America and early Sunday morning for Europe and Africa.

Eclipse Overview | Minute-by-Minute Guide | All about the Moon

Next: So why don't they occur every month?