The earth has a spherical shape, more precisely, itslightly flattened at the edges of the points that are its poles. But this is not particularly noticeable on the scale of the planet, therefore it is assumed that the Earth is a sphere, and its surface is assumed to be spherical.

The layout of the Earth by meridians and parallels yieldedthe ability to accurately determine the coordinates of any object that moves (airplane, storm clouds), or which occupies a certain place on the planet (city, island). This gave quite a lot of advantages for any objects moving in space. Previously, people were guided by the stars, according to the position of the sun in the sky. It was not as accurate as using modern technologies, although if you suddenly find yourself on a desert island without the tools that are so familiar in our life - smartphones, tablets, laptops, respectively, without access to the Internet, without a navigator and other, then it would not be superfluous to know those very "inconvenient" methods of calculating coordinates.

You can use a navigation system in whichthe required coordinates will be entered, and autopilot devices will be able to move themselves where necessary, without a human being. But first things first. Consider the main points and circles on the globe.

## Some historical information

Questions about the coordinates of the minds of people for a long time,even before our era. Outstanding scientists in the development of the coordinate system were Hipparchus and Ptolemy. These people lived in the second and first centuries BC, but, nevertheless, already with separative accuracy could determine the coordinates of the stars. They were great people of their era, powerful geographers and astronomers. It was they who introduced the concept, which we now call the coordinate system, and it becomes clear from their work what geographical coordinates are. At that time, these people did not know that the Earth revolves around the Sun. Hipparchus proposed that the surface of our planet can be considered an ideal sphere, and on its example he explained the various foundations concerning spherical geometry.

## The Globe is the most accurate model of the Earth

It is with the help of the globe that it is easy to determinecoordinates of any country, island or other object. With his help, it's easiest to show what the meridians and parallels are, geographic poles, other points and lines of the Earth.

By the way, the first globe was created a long time ago,even before our era, and it was made by a certain Maltese Kratos in 150 BC, at the same time when Hipparchus and Ptolemy lived. Of course, the globe can not demonstrate all the small details, but in general it allows us to perfectly describe the overall picture of what our planet is, and it perfectly demonstrates, for example, which points of the earth are called geographic poles,

On the globe it's easy to see where theany country, the sea, the ocean, the location of the continents or even their terrain. It depends on what will be shown by the creator of this or that globe. It can be purely political, only with the division of continents into countries and with the indication of large objects such as the oceans. Most likely, it will be a small decorative globe. Training copies contain much more information about the geographical poles and geographical location of any part of the world.

In general, three parameters are distinguished, according to which the Earth is characterized geographically-coordinate plan. Therefore, consider the main points, lines and planes on the surface of the Earth.

## What is the Earth's axis?

Whether to take the Earth for a ball, it becomes clear,that he has such a line, which in the stereometric figure serves instrumental. What exactly is it about? It is a line that is a diameter, rotating around which a semicircle creates a whole sphere. What diameter in comparison with the Earth is called the axis. This is an imaginary line that does not exist in reality, but around it there is a daily rotation, and it is commonly assumed that it passes through the North and South Pole.

## Pole of the planet Earth

What points of the earth are called geographicalpoles? They are all known cold uninhabited northern and southern poles. In stereometry, what is called a "geographical pole" is the point at which the axis of rotation of the earth (the diagonal of the spherical body) intersects with the sphere. The last one in this case is the surface of the Earth.

All these meridians pass through these two poles, which we shall discuss below.

## What are parallels?

Let us continue to consider the Earth as a sphere andwe determine what the parallels are in this case. Assuming that the planet, like the ball, has a center, the axis of the Earth will pass through it and be divided into two equal parts, like the diameter of the radii.

If we draw a certain plane that will bepass perpendicular to the axis, it will cross the sphere along a certain circle, that is, the Earth along a line called the parallel. A parallel having the largest diameter passes through the center of the ball of the Earth, which is a large circle and is called the equator. He divides the sphere into two equal hemispheres. All analogous circles that are created by planes perpendicular to the axis are also called parallels, but are small circles in comparison with the equator. And the lines passing through the poles are geographic, they will be called meridians. By the way, it is thanks to the equator that our Earth is divided into two parts - the northern and southern ones. Accordingly, there are geographic poles of the planet Earth, which are named according to which part of the world they are in.

## Meridian

If we draw a large plane through the axis andthrough the poles, we get as a result a circle called the "full meridian". All meridians are the same in length, as they pass through a straight line and two points on it in different planes. Only their location changes.

The system of meridians and parallels, which are depicted on the map and on the globe, is a degree network.

It is two-dimensional, since onlytwo coordinates - the coordinate of the parallel and the latitude coordinate. What is geographical coordinates? These are two numbers, latitude and longitude. Such numbers have dimensions in degrees and minutes.

At the beginning of the article it was said that the Earth is not quiteThe sphere that it is a little flattened. In what way is this expressed? The length of the equator is 40075.7 kilometers, when the length of the meridian is 40008.5 kilometers. The poles are slightly closer to the equator, although this is not very noticeable on the scale of the planet.

## Planes of the earth spheroid

These are the imaginary planes thatrun parallel or perpendicular to the earth's axis, are the main ones. The area of the plane that passes through the meridian is called, respectively, the plane of the earth's meridian. The most prominent of these is the Greenwich Meridian. It divides the earth into the eastern and western hemispheres. The main plane that passes through the equator and divides the earth into two parts is the Northern and Southern Hemispheres.

## Initial reference lines

All coordinates are calculated using the usualstereometry. We chose the reference points, more precisely, the reference meridian and the reference parallel, from which the coordinates of any place on the Earth are calculated. The zero meridian was chosen one that passes through London, namely through the Greenwich Observatory. As a line, which is considered the origin of the latitude, it is customary to take the longest meridian - the equator.

An interesting fact about the Greenwich meridian.There is a system for assigning coordinates to a point, and it's called the World Geodetic System-84, or WGS-84 for short, (84 is the system year) that the whole world uses, and in which the zero meridian is the ERS Reference Meridian, passing near Greenwich, only 5.31 corner minutes to the east.

## Which lines of the Earth give the width and longitude

Children at school often confuse these concepts - meridiansand a parallel, which of them is the width, and that is the longitude. So, the equator is the origin of latitude, when the Greenwich meridian is the starting line for calculating the longitude.

Geographic latitude can range from 0up to 90 degrees. Depending on which side of the equator the point is located, it is assigned the value of the northern latitude or the southern one. So, let's say, New York has a latitude of 40 degrees 43 minutes of northern latitude, and Sydney has 33 degrees 52 minutes south latitude. It is written down as follows: 40^{about} 43 ', 33^{about }52 '.

Similarly with geographic longitude.It can also be calculated by degrees and minutes, just longitude has a range of values from 0 to 180 degrees. It can be western if it goes west from the zero meridian, and east (similarly - to the east of the zero meridian).

As previously stated, the zero meridian passesthrough Greenwich and has a value of 0 degrees. And which points of the Earth are called the geographic poles of the planet and what are their coordinates? These are the points that are ninety degrees in latitude and zero degrees in longitude.

## Let's sum up the results

On planet Earth, as on the sphere, there are majorpoints, lines and planes. What points of the earth are called geographic poles, we have already figured out. These are the points through which the axis of the diurnal rotation of the Earth passes. If a plane passes through this axis and intersects geographic poles, then it forms the intersection of the sphere of the Earth, which are called meridians.

There is a zero meridian passing inLondon, and a few others, which have the dimension to 180 degrees (there may be at least 180). If a certain plane passes through the axis of rotation of the Earth, namely, perpendicular to it, then their intersection with the Earth's sphere is a parallel. The parallel that has the greatest longitude is called the equator. That he is the starting point for reference latitude. All coordinates are measured in degrees and smaller fractions - minutes, seconds. There are sixty minutes in one degree, and sixty seconds in one minute. Two seconds are used to mark seconds (such as minutes).