Equator and Meridians

Parallels of latitude and Meridians of Longitudes are the two components of Position Reference System. In this lesson, we shall learn about the Equator and Meridians . Equator serves as the Datum Reference for measurement of Latitudes. In our earlier post, we had learnt about the properties of Great Circles.


Equator is a Great Circle whose plane is perpendicular to the Axis of Rotation of earth. On the other hand Meridians are semi-great circles joining the poles. Just like other Great Circles, the Equator also cuts the earth into two equal halves.

These two equal halves of the earth formed by the equator are called as Hemispheres. The hemisphere which is between the Equator and North Pole is called as the Northern Hemisphere and the one between the Equator and South Pole is called as the Southern Hemisphere.


If you draw a Great Circle joining the poles you get a combination of Meridian and its Anti-Meridian. Therefore, Meridians can be defined as a Semi Great Circle joining the poles. The Meridian which is exactly on the opposite side of a certain Meridian is called its Anti-Meridian. A combination of Meridians and Anti-Meridians form a Great Circle.


There is an observatory in a place named Greenwich near London. The Meridian passing through Greenwich is taken as datum for measurement of other Meridians. Therefore, it is called as the Prime Meridian.

We have learnt that Great Circles are circles drawn on the surface of earth with their centre and radius same as that of earth. Equator and Meridians are perfect examples of a Great Circles.

Both the Equator and Meridians would cut the earth into two equal halves. Their difference lies in the fact that Equatorial Plane is perpendicular to the Axis of Rotation of earth. Whereas, the plane of any Meridian is parallel to the Axis of Rotation of earth.

In this post we have learnt about the Equator which forms the basis of latitude Measurement. In our next lesson, we shall understand about the Parallels of Latitude.