9) Eclipse time limits

Columbus knew that lunar eclipses don't go on forever. Astronomers say none can last more than 3 hours and 40 minutes. Totality -- when the Moon is completely immersed in shadow -- cannot run more than 1 hour and 40 minutes.

The period of totality for the Oct. 27, 2004 eclipse will be 1 hour and 22 minutes.

An eclipse on Nov. 8, 2003 had a period of totality just 25 minutes long [Photos].

Why the difference? Earth's shadow is cone-shaped. Envision a slice of it, a two-dimensional circle through which the Moon can pass. Longer stretches of totality mean the Moon is traversing the center of the circle. Shorter total eclipses occur when the Moon's path is nearer the top or the bottom of the shadow.

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

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