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Name: Sam H.
Status: educator
Age: 30s
Location: N/A
Country: N/A
Date: Tuesday, February 18, 2003

Hello, With the sun at the first focus of the planets' elliptical orbit, where (in miles from the sun) is the second empty focus?

That depends on how flat the ellipse is. Ellipses are symmetrical about their major and minor axes; two foci of the ellipse are the same distance, in opposite directions, from the minor axis. To find the answer to your question, you would have to know enough specifying information about the elliptical orbit itself. This would be the lengths of the major and minor axes, or the difference in distance between the distance from the sun to the planet at closest approach and greatest separation.

Richard E. Barrans Jr., Ph.D.
PG Research Foundation, Darien, Illinois

The distance between the sun and the earth varies between about 91.5 million miles and 94.5 million miles. The difference between these two distances is just the distance between the two foci, as I'm sure you can convince yourself if you draw a picture an ellipse. Note that when the earth is 94.5 million miles from the sun, it is just 91.5 million miles from the empty focus. So the second empty focus is just 3 million miles from the sun.

Best, Dick Plano,

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