Solar System

In this post, we would learn a little about the Solar System. We are aware that the earth spins around itself and also revolves around the sun. In our earlier post we had discussed about the Shape of Earth.


The Three Dimensional Plane on which the earth revolves around the sun is called its Orbital Plane. In fact, all the planets in our Solar System revolve around the sun in the same orbital plane. We have seen earlier that the Axis of Rotation of earth is called the Spin Axis. The three dimensional plane of the Rquator is called as the Plane of Equinoxial.

The plane of Equinoxial is exactly perpendicular to the Spin Axis. However, the Spin Axis is not exactly perpendicular or at 90 degrees to the Orbital Plane. The Spin Axis is tilted at an angle of 23 1/2 degrees to the Orbital Plane. This also means that the Plane of Equinoxial and Orbital Plane makes an angle of 23 1/2 degrees. This tilt of the Spin Axis is called the Obliquity of the Ecliptic.

Obliquity of the Ecliptic is not so important for navigation as it makes no difference to our calculations. However, in Meteorology lessons, you would learn that this is one of the main reasons for changing seasons. The amount of sunlight received at a certain place on earth’s surface varies with seasons due to the tilt of spin axis.

Obliquity of the ecliptic plays an important role in changes in duration of daylight depending on seasons. In the next lesson, we shall understand about the Measurement of Directions.