Question

State the nature of shape of orbits of planets.

Answer 1

Hint:Recall Kepler’s first law of planetary motion. The planets do not revolve around the sun in circular orbits. However, the shape of the planet can be almost circular.

Complete answer:
Few centuries ago, there was a belief among our ancestors that all the planets revolved around the earth in the circular orbit until Johannes Kepler formulated the shape of orbits of planets. Kepler formulated three planetary laws. The first law gives the explanation about the nature of the orbits of the planets, the second and third law gives the properties of the paths of the planets.

We know that according to Kepler’s first planetary law, all the planets revolve around the sun in elliptical orbit with the sun remains at one of the foci of the ellipse. Thus, the nature of orbits of the planets is ellipse. We know that the ellipse has two axes: semi-major axis and semi-minor axis. The nature of the orbit of the planet is depicted by the length of the semi-major and semi-minor axis.

We know that the circle is the special case of the ellipse. The orbit of Venus and Neptune is almost circular while the orbit of Pluto (dwarf planet) has the highest eccentricity. It is believed that the cause of elliptical orbits of the planets is due to the gravitational force.

Note: It is not Johannes Kepler who discovered that the planets revolve around the sun and not around the earth. The famous astronomer, Nicolaus Copernicus discovered that the planets revolve around the sun. To answer this type of question, students must recall the laws of planetary motion.