The earth has a spherical shape, or rather, it is slightly flattened. But this is not particularly noticeable on a global scale, so it is assumed that the Earth is a ball and its surface is a sphere. Marking the Earth with meridians and parallels makes it possible to accurately determine the coordinates of any object on the planet.
The globe
Previously, people were guided by the stars, by the position of the sun in the firmament. It was not as accurate as with the help of modern technology, although if you suddenly find yourself on a desert island without a smartphone, without Internet access, it would not be superfluous to know those “inconvenient” methods of calculating coordinates. But first things first. Let’s consider the main points and circles on the globe.
Some historical information
Questions about coordinates have been preoccupying people’s minds for a long time, even before our era. Hipparchus and Ptolemy were outstanding scientists in the development of the coordinate system. These people lived in the second and first centuries BC, but they could already determine the coordinates of the stars. They were great people of their era, powerful geographers and astronomers.
It was they who introduced the concept that we now call the geographical coordinate system. At that time, people did not know that the Earth revolves around the Sun. Hipparchus proposed that the surface of our planet could be considered an ideal sphere, and using its example he explained various fundamentals concerning spherical geometry.
Using a globe, you can easily determine the coordinates of any country, island, or other object. It is also the easiest way to show what the meridians and parallels, geographical poles, and other points and lines of the Earth are. By the way, the first globe was created a long time ago, even before our era, and it was made by a certain Kratet Mallsky in 150 BC, at the same time when Hipparchus and Ptolemy lived.
It is easy to see on the globe where any country, ocean, continent and even their relief are located, depending on what will be depicted by the creator of the globe. It can be purely political, only with the division of continents into countries and with the indication of large objects such as seas and oceans. Others contain much more information about any part of the world.
What are latitudes and meridians?
Latitude and longitude
If you take the Earth for a ball, then it becomes clear that it has an axis. What exactly is it about? This is a line that is the diameter around which the Earth rotates. This is an imaginary line, but the planet rotates around it daily, and it passes through the Earth’s surface at the North and South Poles.
The Earth’s surface is an almost circular sphere. If we assume that the planet, like the ball, has a center, then the Earth’s axis will pass through it and divide into two equal parts, like the diameter into radii. If you draw a plane that runs perpendicular to the axis, it will intersect the sphere along a circle, that is, the surface of the Earth along a line called a parallel.
The parallel with the largest diameter passes through the center of the Earth’s globe and is called the equator. It divides the sphere into two equal hemispheres. All the circles that are created by planes perpendicular to the axis are also called parallels, but they are smaller than the equator. And the lines passing through the geographical poles will be called meridians.
By the way, it is thanks to the equator that our Earth is divided into two parts – the northern and the southern. Accordingly, there are geographical poles of the planet Earth, which are named depending on which part of the world they are located in. If we draw a large plane through the axis itself and through the poles, we get a circle as a result, which is called the “full meridian”.
All meridians are the same in length, as they pass through both poles. Only their location changes. The system of meridians and parallels, which are depicted on maps and a globe, is a degree network. It is two–dimensional because it is defined by two coordinates – latitude and longitude.
What are geographical coordinates?
These are two numbers representing latitude and longitude. Such numbers have a dimension in degrees and minutes. At the beginning of the article, it was said that the Earth is not exactly a sphere, that it is slightly flattened. What does this mean? The poles are slightly closer to the equator, although this is not very noticeable on a global scale.
It is those planes that run perpendicular to the Earth’s axis or through the axis itself that form latitudes and meridians when they intersect with the Earth’s surface. The most famous of them is the Greenwich Meridian, which has a value of 0 degrees longitude. It divides the Earth into the eastern and western hemispheres. And the plane that passes through the equator divides the earth into two parts: the Northern and Southern Hemispheres.
The zero meridian was chosen, which passes through the Greenwich Observatory in London, it has a value of 0 degrees longitude. As a line, which is considered the beginning of the geographical latitude, it is customary to take the equator, which has a value of 0 degrees. The poles of the Earth have a value of 90 degrees north or south latitude. But they do not have a specific longitude value, since all the meridians pass through them.
Geographic latitude can have values from 0 to 90 degrees. Depending on which side of the equator the point is located, it is assigned a value of north or south longitude. Similarly with geographical longitude. It can also be calculated using degrees and minutes, only longitude has a range of values from 0 to 180 degrees. It can be western if it goes west of the prime meridian, or eastern on the contrary.
