1.1 Oval, quadratic closed curve.
1.2 An ellipse is the intersection of a cone with an inclined plane
1.3 Ellipse area
A = π x a x b
a and b are minor and major axis
1.4 The orbit of each planet in the solar system is an ellipse
In the time, the Sun, Moon and planets were assumed to have a perfect circular orbits. Johannes Kepler (1571 - 1630) rejected the idea of circular planetary orbits, and ended up the idea of their elliptical paths, as known nowadays
1.5 Five possible cross-section of the cone which is known for thousands of years.
- point - circle - ellipse - hyperbola - parabola
1.6 The sum of distances from two poinst is equal to major axis.
Points are two foci of the ellipse