Changes

A whisper at one focal point is easily heard at the the other focal point, because the sound waves bounce off the walls and combine again at the other focal point.

A whisper at one focal point is easily heard at the the other focal point, because the sound waves bounce off the walls and combine again at the other focal point.

Ellipses became important in [[astronomy]] in the early 1600s, when [[Kepler]] proved that planets orbiting the sun always follow elliptical paths. This helped overturn the [[Ptolmaic theory]], and led to [[Issac Newton]]'s [[law of gravitation]].  

Ellipses became important in [[astronomy]] in the early 1600s, when [[Kepler]] proved that planets orbiting the sun always follow elliptical paths. This helped overturn the [[Ptolemaic theory]], and led to [[Issac Newton]]'s [[law of gravitation]].  

The orbits of planets observable in Kepler's times were very circular. Comets, on the other hand, have highly eccentric orbits with only one focal point inside the sun.

The orbits of planets observable in Kepler's times were very circular. Comets, on the other hand, have highly eccentric orbits with only one focal point inside the sun.