Kepler's Distance Law

Submitted by Peter L. Griffiths (United Kingdom), Dec 24, 2016 at 11:24

The pins and thread method of constructing the cylindric section was discovered by Kepler in 1604 and has the formula b^2 + (a-f)^2 = a^2, where f is the focus, a is half the major axis, and b is half the minor axis. This formula can also be applied less accurately to closed ellipses, and seemed to be confirmed by Kepler's discovery of the location of the Sun at the focus in 1618. To day 400 years later, and we still cannot evaluate a and b.

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