What are meridians and parallels? How to determine meridians and parallels? Meridians and parallels of the Ural Mountains. &14. Parallels and meridians. Graticule

We remember: What is called the equator? What is the length of the earth's equator? What points on Earth are called geographic poles?

Keywords:equator, parallels, meridians, prime meridian, hemisphere, degree grid, geographic location.

1. Parallels. Have you already remembered that e c v a t o r- this is a line conventionally drawn on the earth's surface at the same distance from the poles. He divides Earth to the Northern and Southern Hemispheres (Fig. 42).

Rice. 42. Hemispheres of the Earth. What separates the Western and Eastern, Northern and Southern hemispheres?

Parallels are lines that are conventionally drawn on the surface of the Earth parallel to the equator. The word "parallel" indicates the position of this line relative to the equator: all points of one parallel are at the same distance from the equator. As you can see on the globe in the form of a parallel - a circle, their length decreases from the equator to the poles. The largest parallel is the equator. A parallel can be drawn through any point earth's surface. Each parallel is directed from west to east (Fig. 43).

Rice. 43. Parallels. Rice. 44. Meridians.

Meridians. The shortest lines conventionally drawn on the surface of the Earth from one pole to another are called meridians (Fig. 44). The direction of the meridian at any point on the earth's surface is most simply determined through the direction of the shadow from objects at noon. Therefore, the meridian is also called the noon line (Fig. 46). Translated from Latin into Russian, the word "meridian" means "midday line".

Figure 46. The meridian line coincides with the direction of the shadow from objects at noon.

Meridians indicate the exact direction from north to south. At each point, the meridian is perpendicular to the parallels, which is why they form a right angle (90 °) with each other. Therefore, if you become facing north, that is, in the direction of the meridian, and spread your arms to the sides, they will indicate the direction of the parallel.

Like a parallel, a meridian can be drawn through any point on the earth's surface.

One of the meridians is conditionally considered to be the initial, or zero. By international agreement 1884, the Greenwich meridian passing through the Greenwich Observatory in London is considered the initial one. The initial meridian divides the globe into two hemispheres - Western and Eastern (Fig. 42).

3. Degree grid. On a globe and maps, meridians and parallels are drawn through the same number of degrees. For example, after 10 0 or 15 0 . (Find these symbols on the globe and map). Intersecting, parallels and meridians form a degree grid on the globe and maps (Fig. 45).

Rice. 45. Degree grid.

* On a globe, parallels and meridians intersect at right angles. When these angles on the map are greater or less than a straight line, this indicates distortion of angles and directions, and hence the shape of objects. On the globe, all meridians have the same length, and the length of the parallels decreases from the equator to the poles, which is true. Violation of this on the map indicates a distortion of distances, and, consequently, areas.

1. What is called a parallel? Meridian? Degree grid? 2. What hemispheres does the equator and the prime meridian divide the globe into? What hemisphere is your area in?

3* Copy table 2 in a notebook and fill it out (instead of a question, write down the answer).

Table 2.

Graticule

Practical work.

1. Find any meridian on a globe or on a map of the hemispheres and determine which continents and oceans it crosses from south to north. 2. Show any parallel and determine which continents and oceans it crosses from west to east.

Almost all of you have paid attention to the "mysterious lines" on maps and globes representing latitude (parallels) and longitude (meridians). They form a grid system of coordinates by which any place on Earth can be precisely defined - and there is nothing mysterious or complicated about it. Parallels and meridians are imaginary lines on the surface of the Earth, and latitude and longitude are their coordinates that determine the position of points on the surface of the Earth. Any point on Earth is the intersection of a parallel and a meridian with coordinates of latitude and longitude. This can be most clearly studied with the help of a globe, where these lines are indicated.
But first, everything is in order. Two places on the Earth are determined by its rotation around its own axis - these are Northern and South Pole A. On globes, the pivot is the axis. North Pole is located in the Arctic Ocean, which is covered sea ​​ice, and researchers in the old days reached this pole on a sleigh with dogs (it is officially believed that the North Pole was discovered in 1909 by the American Robert Perry). However, since the ice moves slowly, the North Pole is not an actual, but rather a mathematical entity. The South Pole, on the other side of the planet, has a permanent physical location on the continent of Antarctica, which was also discovered by land explorers (Norwegian expedition led by Roald Amundsen in 1911).

Halfway between the poles at the "waist" of the Earth is a large circle line, which is represented on the globe as a seam: the junction of the northern and southern hemispheres; this circle line is called - equator. The equator is a line of latitude with a value of zero (0°). Parallel to the equator above and below it are other lines of the circle - these are other latitudes of the Earth. Each latitude has a numerical value, and the scale of these values ​​is not measured in kilometers, but in degrees north and south of the equator to the poles. The poles have meanings: North +90°, and South -90°. Latitudes above the equator are called northern latitudes, and below the equator southern latitudes. Lines with degrees of latitude are called parallels, since they run parallel to the Equator and are parallel to each other. If parallels are measured in kilometers, then the lengths of different parallels will be different - they increase when approaching the equator and decrease towards the poles. All points of the same parallel have the same latitude, but different longitudes (the description of longitude is just below). The distance between two parallels that differ by 1° is 111.11 km. On the globe, as well as on many maps, the distance (interval) from a latitude to another latitude is usually 15° (that's about 1,666 km). In figure No. 1, the interval is 10 ° (this is approximately 1,111 km). The equator is the longest parallel, its length is 40,075.7 km.

Globe and geographic Maps"entangled" in a kind of grid consisting of intersecting lines. These lines did not appear on the maps immediately, since in ancient times the maps resembled the simplest plans.

The globe and the planes of its section

The earth is a sphere slightly flattened at the poles. The sphere can be cut by planes in 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 the ball by 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 sphere.

Let us turn to and mentally dissect the globe with planes perpendicular to the axis of rotation of the Earth. Circles parallel to each other appear on the surface of the globe. These circles are called parallels (from Greek word parallclos - walking beside). The longest and main parallel is the equator, its length is 40,076 kilometers.

The equator is equidistant from the poles of the planet and divides the Earth into Northern and Southern hemispheres. The length of other parallels decreases in the direction from the equator to the south and to the north. All points lying on the same parallel are equally distant from the equator. The lines of parallels 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 from objects at noon.

All meridians have the same length - 20,005 kilometers. By agreement between the countries, the main, initial meridian is considered to be the meridian passing through the Greenwich Observatory in the suburbs of London. Therefore, this meridian is also called the Greenwich meridian. Greenwich meridian and its continuation on the opposite side
of the globe divide the Earth into 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 the convex surface of the Earth is transferred to a plane, the image of these lines looks different. Whatever the form 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 you to navigate, that is, determine directions to the sides of the horizon.

Lines of parallels and meridians on the globe and maps can be drawn as many as you like. But only one meridian and one parallel passes through one point of the surface. The position of any point on a flat sheet can be characterized by two numbers of coordinates 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 prime meridian. To do this, use the system of parallels and meridians.

In the IV century. BC e. the greatest thinker of antiquity, Aristotle, proved that our planet has a shape very close to the shape of a ball.

At about the same time, while observing the visible movement of stars and the Sun during their travels in various places, ancient scientists established certain conditional lines for orientation on the earth's surface.

Let's go on a mental journey on the surface of the Earth. The position above the horizon of the imaginary axis of the world, around which the firmament rotates daily, will change for us all the time. In accordance with this, the picture of the movement of the starry sky will also change.

Going north, we will see that the stars in the southern part of the sky rise to a lower height each night. And the stars in the northern part - in the lower climax - have great height. Moving long enough, we will get to the North Pole. Not a single star rises or falls here at all. It will seem to us that the entire sky is slowly spinning parallel to the horizon.

Ancient travelers did not know that the apparent movement of the stars is a reflection of the rotation of the Earth. And they haven't been to the Pole. But they needed to have a reference point on the earth's surface. And they chose for this purpose the north-south line, easily identifiable by the stars. This line is called the meridian.

Meridians can be drawn through any point on the surface of the Earth. Many meridians form a system of imaginary lines connecting the North and South Poles of the Earth, which are convenient to use to determine the location.

Let's take one of the meridians as the initial one. The position of any other meridian in this case will be known if the reference direction is specified and dihedral angle between the desired meridian and the initial one.

At present, by international agreement, it has been agreed to consider the initial meridian that passes through one of the oldest astronomical observatories in the world - the Greenwich Observatory, located on the outskirts of London. The angle formed by any meridian with the initial is called longitude. The longitude, for example, of the meridian of Moscow is 37° east of Greenwich.

To distinguish points lying on the same meridian from each other, it was necessary to introduce a second geographical coordinate - latitude. Latitude is the angle that a vertical line drawn at a given place on the Earth's surface forms with the plane of the equator.

The terms longitude and latitude have come down to us from ancient sailors who described the length and width mediterranean sea. The coordinate that corresponded to the measurements of the length of the Mediterranean Sea became longitude, and the one that corresponded to the width became the modern latitude.

Finding latitude, like determining the direction of the meridian, is closely related to the movement of stars. Already ancient astronomers proved that the height of the celestial pole above the horizon is exactly equal to the latitude of the place.

Let us assume that the Earth has the shape of a regular ball, and cut it along one of the meridians, as in the figure. Let the person shown in the figure as a light figure stand at the North Pole. For him, the upward direction, that is, the direction of the plumb line, coincides with the axis of the world. The pole of the world is right above his head. The height of the celestial pole is here 90 .

Since the apparent rotation of stars around the axis of the world is a reflection of the real rotation of the Earth, then at any point on the Earth, as we already know, the direction of the axis of the world remains parallel to the direction of the axis of rotation of the Earth. The direction of the plumb line changes when moving from point to point.

Take, for example, another person (in the figure - a dark figure). The direction of the axis of the world remained the same for him as for the first one. And the direction of the plumb line has changed. Therefore, the height of the celestial pole above the horizon here is not 90°, but much less.

From simple geometric considerations it is clear that the height of the celestial pole above the horizon (in the figure, the angle ft) is indeed equal to the latitude (angle φ).

A line connecting points of equal latitude is called a parallel.

Meridians and parallels form the so-called system geographical coordinates. Every point on the earth's surface has a well-defined longitude and latitude. Conversely, if the latitude and longitude are known, then one parallel and one meridian can be built, at the intersection of which one single point will be obtained.

Understanding the features of the daily motion of stars and the introduction of a system of geographical coordinates made it possible to carry out the first determination of the Earth's radius. It was completed in the second half of the 3rd century. BC e. famous mathematician and geographer Eratosthenes.

The principle of this definition is as follows. Let it be possible to measure the difference in latitudes of two points lying on the same meridian (see Fig.). Thus, we became aware of the angle Df with the apex at the center of the Earth, which corresponds to the arc of the meridian L on the Earth's surface. If now we can also measure the arc L, then we will get a sector with a known arc length and corresponding to it central corner. This sector is shown separately in the figure. By simple calculations, you can get the value of the radius of this sector, which is the radius of the Earth.

Eratosthenes, a Greek by nationality, lived in the wealthy Egyptian city of Alexandria. To the south of Alexandria was another city - Siena, which today is called Aswan and where, as is known, with the help of Soviet Union the famous high-rise dam was built. Eratosthenes knew that Siena had interesting feature. At noon one of June days The sun over Siena is so high that its reflection can be seen at the bottom of even very deep wells. From this Eratosthenes concluded that the height of the Sun in Syene on that day was exactly 90°. In addition, since Siena lies strictly south of Alexandria, they are on the same meridian.

For unusual dimension Eratosthenes decided to use scaphis - bowl-shaped sundial with a pin and divisions inside them. Mounted vertically, this sundial measures the Sun's height above the horizon by the shadow of the pin. And at noon on the same day when the Sun rose so high over Siena that all objects ceased to cast shadows. Eratosthenes measured its height in the city square of Alexandria. The altitude of the Sun in Alexandria, according to the measurements of Eratosthenes, turned out to be 82° 48". Therefore, the difference between the latitudes of Alexandria and Syene is 90° 00" - 82° 48" = 7° 12".

It remained to measure the distance between them. But how to do that? How to measure on the surface of the Earth a distance equal to modern units about 800 km?

The difficulties of such an undertaking were then literally incalculable.

Indeed, how to make such a gigantic ruler with which one could make measurements? How to make this line fit strictly along the meridian for 800 km, without any distortions?

The necessary data on the distance between cities had to be taken from the stories of merchants who drove trade caravans from Alexandria to Siena. The merchants said that the distance between them was about 5,000 Greek stadia. Eratosthenes accepted this value as true and, using it, calculated the value of the radius of the Earth.

If we compare the value obtained by Eratosthenes with modern data, it turns out that he was mistaken relatively little - only by 100 km.

So, from the III century. BC e., since the time of Eratosthenes, the paths of astronomy and geodesy have intertwined - another ancient science, which studies the shape and size of both the entire Earth as a whole and its individual parts.

Methods for astronomical determination of latitudes have been developed and improved. This was especially important, in particular, precisely in connection with the need for a more thorough determination of the size of the Earth. For, starting with the same Eratosthenes, it was understood that the problem of determining the size of the Earth falls into two parts: astronomical, that is, determining the difference in latitudes, and geodesic, that is, determining the length of the meridian arc. Eratosthenes managed to solve the astronomical part of the problem, and many of his followers followed the same path in principle.

We shall have occasion to tell more about accurate measurements the size of the Earth, but for now, having mastered the definition of latitudes, let's deal with a much more complicated matter - the definition of geographical longitudes.

“And cities and countries, parallels, meridians flash by,” is sung in a song called “Globe”. But if the cities and countries indicated on the globe exist in reality, then the parallels and meridians are imaginary objects marked on the globe or map solely for ease of reading and orientation.

The best assistant in orientation is a coordinate system, which must have a reference point. The Earth (however, the same principle can be applied to any other planet or its satellite - it would be, for what) such an imaginary "zero point" was determined using poles - points through which the axis of its rotation passes. The North Pole is a rather mathematical object, it is located in the North Arctic Ocean, but the South Pole is a very real point on land, on the mainland called Antarctica, you can get there, you can take pictures there - if you are not afraid to freeze, of course ...

So, at an equal distance from these very poles, in the middle between them, there is an imaginary "belt" of the Earth, dividing the planet in half, into the Northern and Southern hemispheres. Most of the continents are in one of them, and only Africa is in both. So, the equator is the “reference point”, which is considered zero latitude. Imaginary lines drawn on a map and globe parallel to the equator are called parallels.

Latitude is measured in degrees, 1 degree is approximately 111 km. It is considered from the equator (the farther from it, the more number: equator - 0 degrees, poles - 90 degrees). Degrees are measured north of the equator northern latitude, to the south - east longitude. There is another way to designate: south of the equator, latitude is written with a minus sign (this can be understood: those who created geographical science lived in the Northern Hemisphere, and their shirt, as you know, is closer to the body).

All this, of course, is wonderful, but ...

Let us recall the novel by J. Verne "Children of Captain Grant". The heroes who went to help Captain Grant and his companions, who survived the shipwreck, knew that their location was thirty-seven degrees eleven minutes south latitude. To find them, the heroes had to travel around the world along this parallel.

To avoid such difficulties, there is a second coordinate - longitude, and on the map it is indicated by meridians - lines connecting the poles.

If we wanted to choose a parallel for the longest world travel, it would certainly be the equator. But choosing a meridian for such a thing will not work - they are approximately the same, so choosing a starting point among them is not so easy, therefore for a long time in this regard, there was discord: in France, the Parisian meridian was taken as a reference point, in Russia - passing through the Pulkovo observatory, etc. Finally, in 1884, on International Conference in Washington, they adopted a single reference point - the meridian passing through the axis of the transit instrument of the observatory in Greenwich - administrative district London on the right bank of the Thames. It is from the Greenwich meridian that the western and eastern longitudes are calculated (the heroes of the mentioned novel were not lucky: the longitude in the note was washed away with water).

The number of kilometers in one degree of longitude is more difficult to name than in relation to latitude: it is not the same at different latitudes - at the equator it is also 11 km, and the closer to the poles - the less).