[Univ of Cambridge] [Dept of Engineering]

Shadow motion during
Total Lunar Eclipse
3-4 March 2007

Dr Hugh Hunt


Shadow path seen by non-rotating observer ...... Shadow path viewed by observer on Earth

The shadow of the Earth appears to move asymmetrically across the surface of the moon during a total lunar eclipse.

This PDF link shows why.

The shadow of the Earth moved steadily over the surface of the moon over a period of nearly 4 hours (about 220 minutes). A non-rotating observer would have seen the shadow move in a straight line. But we are observing from the Earth rotating 360 degrees in 24 hours, i.e. about 55 degrees in 220 minutes.

Also, for the particular eclipse in March 2007, the centre of the Earth's shadow did not pass over the centre of the moon. This accounts geometrically for another 35 degrees or so.

The total of these two effects explain why the shadow appears to leave from the "side"of the moon - about 90 degrees from where you'd perhaps expect to see it.

Watch the video here.

For gyroscopic things: go to Gyro and boomerang page

and for all sorts of video clips on spinning things go to: Dynamics movies page

and click here for Transit of Venus 8 June 2004, Trinity College Great Court

and for other stuff: go to Hugh Hunt's Cambridge University home page