Elliptical Orbits

Sreeda asks:

1. Why do planets move in elliptical paths and not in circular ones?

Answer: Ellipse is a more general shape than a circle. Circle is a special case of ellipse when its semimajor axis and the semiminor axis are of equal lengths. The shape of orbit depends on various factors. Johannes Kepler in the 1600s was the first to start discussing the shape of planetary orbits, formulating a series of laws to explain their shape and characteristics. Isaac Newton and Albert Einstein contributed additional research and theories. Shape of a planet's orbit is affected by the gravitational force of sun as well as other planets. Also Remember that the sun is also in motion, which makes elliptical orbit an easy one than a perfectly circular one. [Comments solicited from esteemed visitors]