On 2005-10-12, tt40 wrote:
In everything I've read about planets and elliptical orbits, I can't
ever recall any author (Feynman, Newton, 'Ask an Astronomer' etc.),
explaining exactly 'why' the orbit is elliptical. Oh sure there's been
lots of mathematics to explain the orbit and how it works, but most of
the explanations don't provide a definitive statement as to why it IS
elliptical.

Orbits are elliptical because of the inverse square law of gravity and
Newton's three laws of motion. Isaac Newton worked it out in Principia
back in the 17th century.

--
The night is just the shadow of the Earth.