Why do some eclipses take longer than others? (Intermediate)

Why is it that eclipses have different speeds? The solar eclipse in Christmas 2000 took almost three hours; why?

One reason that eclipses take different amounts of time has to do with whether it is a total eclipse or a partial eclipse, and if it's a partial eclipse, what percentage of the sun is actually being covered. For a total eclipse, the entire disk of the moon has to move across the entire disk of the sun before we would say that the eclipse is "over", but for a small partial eclipse the edges of the disks are only going to graze each other, so it will be over quicker.

Another effect has to do with the distance between the earth and the moon. The moon follows an elliptical orbit around the earth, and the distance between the moon and the earth can vary by something on the order of 10 percent, depending on what part of its orbit the moon is in. When the moon is closer to the earth, it is moving faster; plus, its apparent size on the sky is larger. Both of these affect how long an eclipse will take.

This page was last updated June 28, 2015.

About the Author

Dave Rothstein

Dave is a former graduate student and postdoctoral researcher at Cornell who used infrared and X-ray observations and theoretical computer models to study accreting black holes in our Galaxy. He also did most of the development for the former version of the site.

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