Latitudes and Longitudes

Eratosthenes was the first person to calculate the size of the earth. He realized that Earth could be located with a basic grid of lines called Longitudes and Latitudes.

Great Circle

When a sphere is divided exactly in half through its center, the circumference represents the largest circle that can be drawn on that sphere. The shortest distance between two points on a sphere is a great circle, or a circle whose plane passes through the centre of sphere. In case of Earth, only equator is a great circle among latitudes and all longitudes are half great circles.

Latitudes

Latitude is the angle between the equatorial plane and the axis. Lines joining points of the same latitude are called parallels. Equator {0° parallel} itself is largest parallel and only circle of latitude which also is a great circle. Equator is also used as fundamental plane of all geographic coordinate systems. It’s worth note that geostationary satellites are over the equator at a specific point on Earth, so their position related to Earth is expressed in longitude degrees only. Their latitude is always zero.  There are 180° of latitudes and each degree of latitude spans around 111 kilometers or 69 miles or 60 Nautical miles. But this distance varies because Earth is not a perfect sphere.  From Equator to 40° towards both poles it is slightly less than 111 kilometers and from 41° towards both poles it is slightly more than 111 kilometers. The 90° North and 90° South are not circles but only reference points. Latitudes tell us the temperature and climatic position of a particular place.

Longitudes

Longitude is the angle east or west of a reference meridian between the two geographical poles to another meridian that passes through an arbitrary point. All meridians are halves of great circles, and are not parallel to each other. They converge only at the north and south poles. A line passing to the rear of the Royal Observatory, Greenwich (near London in the UK) has been chosen as the international zero-longitude reference line and is known as the Prime Meridian. Places to the east are in the eastern hemisphere, and places to the west are in the western hemisphere. The antipodal meridian of Greenwich serves as both 180°W and 180°E. There are 360° of the meridians and the longitude of prime meridian is 0°. Length of all meridians is equal. The distance between two meridians is farthest at the equator and it decreases as we move towards poles and becomes zero at poles.