The last chance to see a total lunar eclipse for more than two years comes Wednesday evening for most residents of North America and Western Europe.

The event -- which might be televised during World Series Game 4 -- will wrap up a series of four total lunar eclipses in the past 18 months. But there won't be another one for more than two years, on March 3, 2007.

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 shiny 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. [Graphic]

This week's total lunar eclipse starts Wednesday evening in North and South America and, for eastern locations, runs into Thursday morning. In Western Europe, the whole event takes place after midnight. [Timetable]

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

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