The globe and geographical maps are “entangled” in a kind of grid consisting of intersecting lines. These lines did not appear on maps immediately, since in ancient times maps resembled simple plans.
The globe and its section planes
The Earth is a ball slightly flattened at the poles. The ball can be cut by planes along different directions. It can be cut, firstly, in the same way as an orange is divided into slices, and, secondly, in the same way as an orange is cut across the slices with a knife. With any method of dissecting a ball with planes, circles are obtained, the boundaries of which are circles. The diameter of the circles is greatest if the section planes pass through the center of the ball. The diameters of such circles are equal to the diameter of the ball.
Let us turn to and mentally dissect the globe with planes perpendicular to the Earth’s axis of rotation. Circles parallel to each other appear on the surface of the globe. These circles are called parallels (from the Greek word parallclos - walking next to each other). The longest and main parallel is the equator, its length is 40,076 kilometers.
The equator is located at equal distances from the planet's poles and divides the Earth into the Northern and Southern Hemispheres. The length of other parallels decreases towards the south and north from the equator. All points lying on the same parallel are equally distant from the equator. The parallel lines show the west-east direction.
If you cut the globe with planes that pass through the axis of rotation of the Earth, then meridians will appear on the surface of the globe - semicircles connecting the North and South poles of the Earth. They are perpendicular to the parallels and show the north-south direction. The word “meridian” itself means “midday” (from the Latin word meridianus), since the direction of all meridians coincides with the direction of the shadow of objects at noon.
All meridians have the same length - 20,005 kilometers. By agreement between the countries, the main, prime meridian is considered to be the meridian passing through the Greenwich Observatory in the suburbs of London. Therefore, this meridian is also called Greenwich. Greenwich meridian and its continuation on the opposite side
The globe divides the Earth into the Western and Eastern Hemispheres.
Parallels and meridians on maps
The parallels on the globe are circles, and the meridians are semicircles. But due to distortions when transferring the convex surface of the Earth onto a plane, the image of these lines looks different. Whatever the appearance of the parallels and meridians, on any map the directions to the east and west are determined only by the direction of the parallels, and to the north and south - only by the direction of the meridians. Thus, parallels and meridians allow one to orient themselves, that is, determine directions to the sides of the horizon.
You can draw as many lines of parallels and meridians on the globe and maps as you like. But only one meridian and one parallel pass through one point on the surface. The position of any point on a flat sheet can be characterized by two coordinate numbers that show the position of this point relative to the edges of the sheet.
On a spherical surface, the coordinates of points are determined with respect to the equator and the prime meridian. For this, a system of parallels and meridians is used.
There is no clear answer to the question of what a meridian is. Therefore, let's start in order and see in which sciences and in which areas this concept is applied.
The word "meridian" comes from a Latin word that means "noon".
1. Astronomical meridian or, as it is also called, the true meridian. In astronomy, a meridian is a line that passes through both poles of the world, as well as the zenith (the point on the celestial sphere that is directly above the observer’s head) and the nadir (the point that is opposite to the zenith, that is, located directly under the observer’s feet). We have all seen this meridian in astronomy and geography textbooks. All points on this invisible line have the same astronomical longitude
2. The celestial meridian almost always coincides with the astronomical meridian, that is, a line that also passes through the poles of the world and the zenith above the observer’s head.
3. The Greenwich Meridian is, perhaps, the meridian that is known to everyone all over the world. The Royal Observatory Greenwich is the most important and fundamental astronomical organization in England. It was founded in 1675 and since then it has functioned like clockwork. True, today this observatory is a museum, which is the most visited museum in England. It is through this observatory that passes Prime Meridian, which is the beginning of longitude on the globe. This event took place in 1851. For a very long time after this, the prime meridian itself was marked with a special brass ribbon that ran right through the observatory yard. Over time, this tape was replaced with another - made of stainless steel, and today the zero meridian is marked with a green laser beam, which is directed to the north.
4. Geodetic meridian. This meridian is a conventional line that runs along the surface of the earth and all points that are located on it have the same geodetic longitude.
5. The cartographic meridian passes through the axis of rotation of the Earth and is most often drawn on a paper image of the globe.
However, there are many more meridians. These are the names of cities and rivers, nightclubs and music bands, spacecraft and travel companies, newspapers and magazines... Many things in our world are called the word “meridian”. This fashion has not spared our city either. We have a small store proudly called “Meridian”. When I asked a saleswoman I knew why it was called that, she looked at me with incredible surprise, but decided to ask the director.
The next day I received an answer. It turns out, according to the director, a meridian is a place where rays of light converge. And so the buyers are these very rays, and the store is their meeting place. I was a little shocked by this answer, and then asked how old this director was. It turned out that he was 41 years old...
Here is another explanation for what “Meridian” is, although it does not at all fit the celestial or astronomical meridian, but apparently it fits this shop very accurately...
If our planet is “cut” through the axis of rotation and perpendicular to it by many planes, then vertical and horizontal circles - meridians and parallels - will appear on the surface.
The meridians will converge at two points - at the North and South Poles. Parallels, as the name suggests, are parallel to each other. Meridians serve to measure longitude, parallels - latitude.
An action so simple at a superficial glance - “ruling out” the Earth - became the greatest discovery in the study of the planet. It made it possible to use coordinates and accurately describe the location of any object. Without parallels and meridians it is impossible to imagine a single map or a single globe. And they were invented... in the 3rd century BC by the Alexandrian scientist Eratosthenes.
Reference. Eratosthenes had encyclopedic knowledge in all areas at that time. He was in charge of the legendary Library of Alexandria, wrote the work “Geography” and became the founder of geography as a science, compiled the first map of the world and covered it with a degree grid of verticals and horizontals - he invented a coordinate system. He also introduced names for lines - parallel and meridian.
Meridian
In geography, a meridian is half a sectional line of the earth's surface drawn through any point on the surface. All imaginary meridians, of which there can be an infinite number, connect at the poles - North and South. The length of each of them is 20,004,276 meters.
Although you can mentally draw as many meridians as you like, for ease of movement and mapping, their number and location have been regulated by international treaties. In 1884, at the International Meridian Conference in Washington, it was decided that the prime meridian (zero) would be the one that passes through Greenwich, a county in southeast London.
However, not everyone immediately agreed with this decision. For example, in Russia, even after 1884 until the beginning of the twentieth century, the zero meridian was considered to be its own - Pulkovo: it “passes” through the Round Hall of the Pulkovo Observatory.
Prime Meridian
The prime meridian is the starting point of geographic longitude. He himself, accordingly, has zero longitude. This was the case before the creation of the world's first satellite navigation system, Transit. 
With its appearance, the prime meridian had to be shifted slightly - 5.3" relative to Greenwich. This is how the International Reference Meridian appeared, which is used as a reference point for longitude by the International Earth Rotation Service.
Parallel
In geography, parallels are lines of an imaginary section of the surface of the planet by planes that are parallel to the equatorial plane. The parallels depicted on the globe are circles parallel to the equator. They are used to measure geographic latitude.
By analogy with the Greenwich prime meridian, there is also a zero parallel - this is the equator, one of the 5 main parallels, which divides the Earth into hemispheres - southern and northern. Other main parallels are the tropics North and South, the polar circles - North and South.
Equator
The longest parallel is the equator - 40,075,696 m. The rotation speed of our planet at the equator is 465 m/s - this is much greater than the speed of sound in air - 331 m/s.
Southern and Northern tropics
The Tropic of the South, also called the Tropic of Capricorn, is located south of the equator and is the latitude above which the noon sun is at its zenith on the day winter solstice.
The Northern Tropic, also known as the Tropic of Cancer, is located north of the equator and, similar to the southern Tropic, represents the latitude above which the midday sun is at its zenith on the day of the summer solstice.
Arctic Circle and Antarctic Circle
The Arctic Circle is the boundary of the polar day region. To the north of it, in any place at least once a year the sun is visible above the horizon 24 hours a day or not visible for the same amount of time.
The Southern Arctic Circle is similar to the Northern Circle in every way, only it is located in the southern hemisphere.
Degree grid
The intersections of meridians and parallels form a degree grid. Meridians and parallels are spaced at intervals of 10° - 20°; smaller divisions, as in angles, are called minutes and seconds. 
Using a degree grid, we determine the exact location of geographical objects - their geographical coordinates, calculating longitude from meridians, and latitude from parallels.
When looking at the globe, I always pay attention to the lines that, like a huge network, envelop the Earth. These are the parallels and meridians, the introduction of which became a breakthrough in geography. Actually, my story will be about them.
Degree grid of meridians and parallels
Today, this method of determining the location of an object seems elementary, but humanity did not immediately come to it. These lines did not appear all at once, but were the result of a series of discoveries in the field of geography. For example, Aristotle was able to prove that the Earth is a sphere, and ordinary travelers by the stars traced the North-South direction, which, in fact, became the first meridian. Today there are 540 such lines, and together they form a degree grid, which makes it possible to establish the exact location of any object. At the same time, this structure allows you to create detailed atlases, the pages of which show all the details in a certain square. As for the globe, its first models already had both meridians and parallels, which, although not perfect, nevertheless gave an idea of the location of objects.
Parallels and meridians, as well as other map elements
Today, no matter what map you take, the following elements clearly stand out on it:
- Meridians. These lines conditionally divide the Earth into 2 hemispheres: Western and Eastern. At the same time, the starting point is considered to be the zero meridian or, as they sometimes say, the initial meridian.
- Parallels. First of all, there is the equator, which is actually the longest line. With its help, the planet is divided into the Northern and Southern Hemispheres, while the length of the lines following from the equator becomes smaller as it approaches the poles.
- Poles. There are 2 of them - South and North. In fact, these are the points where the imaginary axis of the planet and the beginning of all meridians intersect.
I repeat once again that the division of the surface, as simple as it seems, became a real breakthrough in geography, but who is the genius who came up with this? In the 3rd century BC. this was done by Eratosthenes, one of the greatest geographers of his time.
Coordinates and location of any object on Globe can be determined by knowing the latitude and longitude of a point. Let's find out the subtleties of the meaning of each of them.
How to determine coordinates
Any modern geographic map makes it possible to find the coordinates of any city, mountain or lake. You need to know the latitude and longitude indicators.
With the first, everything is clear: it is determined relative to the equator - an imaginary line that runs at the place where the plane perpendicular to the Earth’s axis intersects the center of our planet. It is the starting point, a kind of “zero” for finding the value of latitude and the location of parallels. The equator passes through several countries - Congo, Kenya, Uganda, Somalia in Africa, Indonesia located in the Sunda Islands, Ecuador, Brazil, Colombia in The equator gives a clear idea of latitude.
Another thing is longitude. For a long time there was no consensus on what to take as the basis for measuring this coordinate. Longitude is the determination of the position of a point on the Earth's surface relative to the zero reference point from which the meridians depart. These are also imaginary lines that make working with maps easier. The angle between each of them and the origin is longitude. The zero meridian is the basis of reference for this coordinate.
The problem of determining longitude
If everything is clear with the equator, then what the “zero meridian” is did not immediately become clear. Long years V different countries used their "zero". Of course, this created confusion.
Every science-respecting country in the 19th century already acquired an observatory for observing celestial bodies. This was the starting point for longitude. Russia, the USA, Great Britain and France had their own initial meridian positions.
Longitude is very important in sea navigation. And long before the formation of clear scientific systems There were other methods of counting that made it possible not to get lost at sea. The first option was proposed by Johann Werner. The essence is observing the Moon. Another method belongs to the genius Galileo Galilei. Using a telescope, he observed the position. The disadvantage of this method is the need for complex instruments.
A simpler method - determination using the difference between local and exact time at a reference point - belongs to the author of Frisius Gemme. But not everyone had such an accurate watch either.
The zero meridian has become a kind of grail - for precise definition longitudes in Britain even offered a huge bonus. Then the problem was the invention of accurate watches. They didn’t know exactly what the prime meridian was then.
Clocks were invented after all. John Harrison received the prize for them. But they continued to use ancient methods in navigation. The turning point was the invention of radio. Modern sailors use satellite data to determine longitude.
Reference points
As already mentioned, every country that had an observatory made it the origin of longitude. The meridian of the same name passes through the Paris Observatory. It was popular in the 19th century.
In Russia, the zero meridian was called Pulkovsky. It received its name from the observatory located near St. Petersburg. Used primarily in Russia. This “zero” meridian passes through Mogilev, the Kyiv region, Lake Tanganyika in Africa, and the pyramids of Egypt. On modern stage not used.
The Ferro meridian, passing through the Canary island of the same name, was popular. First used by Ptolemy.
Since the 19th century, England has used the Greenwich meridian. It has become established as a “zero” for measuring longitude in the modern world.
The Greenwich Prime Meridian is an imaginary line through London. With Pulkovsky he has a difference of 30 degrees, with Paris - 2.
Meridial conference
In 1884, eminent geographers and politicians gathered in Washington on the issue of regulating the coordinate reference system. The International Meridial Conference brought together representatives from Russia, Austria-Hungary, Germany, Great Britain, France, Denmark, Chile, Venezuela, Japan, Switzerland, Ottoman Empire and many other countries. A total of 41 representatives attended.
In addition to determining longitude, participants were interested in developing a time system. What is the problem? And the fact is that until the 19th century there was no single unified time. Everyone used local units. This caused confusion. Lack of standards hindered trade between countries with different levels development of science and culture. There were also problems with transport.
Where should longitude begin?
Of all the already existing starting points, it was necessary to choose one. The decision was made by open voting, in which all delegates present participated.
At the conference they decided which object should become the starting point for longitude. The zero meridian, according to the proposals of the delegates, could pass through Paris, the Azores or Canary Islands, the Bering Strait, and Greenwich. The islands immediately lost in votes - they did not have the proper level of scientific support. Paris didn't get any votes either. Ferro, although popular, was also rejected. London's Prime Meridian was the winner, with only France objecting.
A little about time
The first person to talk about the need to unify time standards was Mr. Sandford Fleming, a simple Canadian engineer. One day, due to time confusion, he missed the train and missed an important meeting. Thus, from 1876, Fleming sought reform.
The issue was resolved at the above-mentioned conference in Washington. A time zone system was formed, which is still used today. Not everyone accepted the innovations. For example, Russia joined the standard only in 1919. Germany, France and Austria-Hungary also joined later.
The origin is the prime meridian. This imaginary line runs through oceans, seas, and land. The boundaries of the 24 belts are meridians. However, not everyone still follows this division. The reasons for this are the size of the countries. are also located in Greenwich. By the way, the GPS system shows the beginning of longitude not at the observatory, but 100 meters away from it.
Greenwich Observatory
The center for astronomical research in the UK and the origin of longitude is the Greenwich Observatory. At this place rich story. It was founded in the 17th century through the efforts of King Charles II. During its existence, the observatory changed its location. The very idea of creating such an institution belonged not to the king, but statesman Jonas Moore. He convinced the king of the importance of the observatory, and proposed to make John Flamsteed the chief astronomer. Soon the building was designed and built, with the lion's share of the financing coming from Moore.
An accurate clock and time standard were installed here. As you know, the origin of longitude passes through the observatory. At the local level, the Greenwich Meridian began to be used back in 1851, and was approved at the famous conference in 1884.
They once tried to blow up the observatory! At the time of 1894, this was a unique, first case in British history.
At the present stage, the observatory continues to function. Various instruments for research in the field of astronomy are located here. In fact, this is a museum containing many valuable exhibits. They reflect the history of science and technology, especially in the field of time measurements. Recently a reconstruction was carried out, a planetarium and galleries were created.
Conclusion
The prime meridian is the starting point of longitude and time. But this term can be used in other areas. Thus, in 2006, the “Zero Meridian” group became popular in Russia. “Not my words” - the most famous song this group.
Longitude has been counted from Greenwich for many years. Lines extend from the prime meridian, along which coordinates are determined in all parts of the world. It breaks into the east and passes the prime meridian through Algeria, Ghana, Mali, Spain, Great Britain, France. Thus, these countries are located in both hemispheres at the same time.
