Geographic latitude

Geographic latitude is determined using parallels. Latitude can be northern (those parallels that are north of the equator) and southern (those parallels that are south of the equator). Latitude values ​​are measured in degrees and minutes. Geographic latitude can range from 0 to 90 degrees.

Rice. 1. Determination of latitudes

Geographic latitude– arc length in degrees from the equator to a given point.

To determine the latitude of an object, you need to find the parallel on which this object is located.

For example, the latitude of Moscow is 55 degrees and 45 minutes north latitude, it is written like this: Moscow 55°45"N; latitude of New York - 40°43"N; Sydney – 33°52" S

Geographic longitude

Geographic longitude is determined by meridians. Longitude can be western (from the 0 meridian to the west to the 180 meridian) and eastern (from the 0 meridian to the east to the 180 meridian). Longitude values ​​are measured in degrees and minutes. Geographic longitude can have values ​​from 0 to 180 degrees.

Geographic longitude– length of the equatorial arc in degrees from the prime meridian (0 degrees) to the meridian of a given point.

The prime meridian is considered to be the Greenwich meridian (0 degrees).

Rice. 2. Determination of longitudes

To determine longitude, you need to find the meridian on which a given object is located.

For example, the longitude of Moscow is 37 degrees and 37 minutes east longitude, it is written like this: 37°37" east; the longitude of Mexico City is 99°08" west.

Rice. 3. Geographical latitude and geographic longitude

Geographical coordinates

To accurately determine the location of an object on the surface of the Earth, you need to know its geographic latitude and geographic longitude.

Geographical coordinates – quantities that determine the position of a point on earth's surface using latitudes and longitudes.

For example, Moscow has the following geographic coordinates: 55°45"N and 37°37"E. The city of Beijing has the following coordinates: 39°56′ N. 116°24′ E First the latitude value is recorded.

Sometimes you need to find an object at already given coordinates; to do this, you must first guess in which hemispheres the object is located.

Bibliography

Main

1. Beginner course Geography: Textbook. for 6th grade. general education institutions / T.P. Gerasimova, N.P. Neklyukova. – 10th ed., stereotype. – M.: Bustard, 2010. – 176 p.

2. Geography. 6th grade: atlas. – 3rd ed., stereotype. – M.: Bustard, DIK, 2011. – 32 p.

3. Geography. 6th grade: atlas. – 4th ed., stereotype. – M.: Bustard, DIK, 2013. – 32 p.

4. Geography. 6th grade: cont. cards. – M.: DIK, Bustard, 2012. – 16 p.

Encyclopedias, dictionaries, reference books and statistical collections

1. Geography. Modern illustrated encyclopedia / A.P. Gorkin. – M.: Rosman-Press, 2006. – 624 p.

Materials on the Internet

1. Federal Institute pedagogical measurements ().

2. Russian Geographical Society ().

There are many various systems coordinates. All of them serve to determine the position of points on the earth's surface. These include mainly geographic coordinates, plane rectangular and polar coordinates. In general, coordinates are usually called angular and linear quantities that define points on any surface or in space.

Geographic coordinates are angular values ​​- latitude and longitude - that determine the position of a point on the globe. Geographic latitude is the angle formed by the equatorial plane and a plumb line at a given point on the earth's surface. This angle value shows how far a particular point on the globe is north or south of the equator.

If a point is located in the Northern Hemisphere, then its geographic latitude will be called northern, and if in the Southern Hemisphere - southern latitude. The latitude of points located on the equator is zero degrees, and at the poles (North and South) - 90 degrees.

Geographic longitude is also an angle, but formed by the plane of the meridian taken as the initial (zero) and the plane of the meridian passing through this point. For uniformity of definition, we agreed to consider the prime meridian to be the meridian passing through astronomical observatory in Greenwich (near London) and call it Greenwich.

All points located to the east of it will have eastern longitude (up to the meridian 180 degrees), and to the west of the initial one will have western longitude. The figure below shows how to determine the position of point A on the earth's surface if its geographic coordinates (latitude and longitude) are known.

Note that the difference in longitude of two points on Earth shows not only their mutual arrangement in relation to the prime meridian, but also the difference in these points at the same moment. The fact is that every 15 degrees (24th part of the circle) in longitude is equal to one hour of time. Based on this, it is possible to determine the time difference at these two points using geographic longitude.

For example.

Moscow has a longitude of 37°37′ (east), and Khabarovsk -135°05′, that is, lies east of 97°28′. What time do these cities have at the same moment? Simple calculations show that if it is 13 hours in Moscow, then in Khabarovsk it is 19 hours 30 minutes.

The figure below shows the design of the frame of a sheet of any card. As can be seen from the figure, in the corners of this map the longitude of the meridians and the latitude of the parallels that form the frame of the sheet of this map are written.

On all sides the frame has scales divided into minutes. For both latitude and longitude. Moreover, each minute is divided into 6 equal sections by dots, which correspond to 10 seconds of longitude or latitude.

Thus, in order to determine the latitude of any point M on the map, it is necessary to draw a line through this point, parallel to the lower or upper frame of the map, and read the corresponding degrees, minutes, seconds on the right or left along the latitude scale. In our example, point M has a latitude of 45°31’30”.

Similarly, drawing a vertical line through point M parallel to the lateral (closest to the given point) meridian of the border of a given sheet of the map, we read the longitude (eastern) equal to 43°31’18”.

Drawing a point on a topographic map at specified geographic coordinates.

Drawing a point on a map at specified geographic coordinates is done in the reverse order. First, the indicated geographic coordinates are found on the scales, and then parallel and perpendicular lines are drawn through them. Their intersection will show a point with the given geographic coordinates.

Based on materials from the book “Map and Compass are My Friends.”
Klimenko A.I.

Astronomy first hand

About our coordinates

N.S.Blinov

Geographic coordinates, latitude and longitude, which determine the position of a point on the earth's surface, were known back in ancient Greece. However, among the Hellenes these concepts were significantly different from our modern ones.

Now we measure latitude in degrees from the equator, and longitude from some arbitrarily chosen meridian, for example, from Greenwich.

The ancients had no idea about degree grid and determined latitude either by the height of the Polar, or by the duration of the longest day of daylight in the year, or by the length of the shortest shadow. It was more difficult with longitude or the difference in longitude, which can only be defined as the difference in local times measured at two points at the same physical moment. The problem was to either somehow deliver the time of one point to another, or to register some phenomenon simultaneously observed from two points. Hipparchus proposed using lunar eclipses as such a phenomenon, but, unfortunately, did not indicate methods for measuring local time. It was impossible to directly use a sundial for this purpose, since during an eclipse of the Moon the Sun is below the horizon. The accuracy of determining the same phase of the eclipse was also very low.

It took about a millennium before people learned to determine latitude and longitude with sufficiently high accuracy.

This problem became especially acute during the era of the great geographical discoveries, when sailors needed knowledge of the coordinates of their ships.

In 1567, the Spanish King Philip II offered a reward for solving the problem of determining longitude on the high seas. In 1598, Philip III promised 6 thousand ducats as a permanent contribution, 2 thousand ducats as a life annuity and 1 thousand ducats to assist anyone who could “discover longitude”.

The United Provinces of Holland awarded a prize of 30 thousand florins. Portugal and Venice also promised rewards.

One of the most famous contenders for longitude prizes was Galileo Galilei. Using the telescope he designed, Galileo observed the eclipses of the moons of Jupiter, compiled tables predicting these eclipses, and proposed using the moments of the eclipses to determine the longitude of the observer.

Navigators, having their local time, say, from observations of the Sun, and knowing from tables the time when eclipses of Jupiter's satellites occur on a certain reference meridian, could calculate the time difference, that is, the longitude of their ship from the reference meridian.

Another, also astronomical, method of determining longitude was proposed: by observing the position of the Moon among the stars. This method, in principle, is similar to Galileo’s method, only in it it was not eclipses of Jupiter’s satellites that were observed, but the distances of the lunar disk from reference, well-known stars were determined. Tables were compiled giving the position of the Moon among the stars on the meridian for a certain point in time.

Unfortunately, both astronomical methods have not found wide application in maritime navigation.

Firstly, they are only possible on clear nights.

Secondly, they require a good theory of the motion of the satellites of Jupiter and the Moon; theories, especially for the Moon, a very capricious luminary, were absent in the 17th-18th centuries.

Thirdly, the moments of eclipse of satellites from the ship are determined with large errors. This also applies to the positions of the Moon among the stars.

Fourthly, astronomical observations require highly trained navigators, which was also not always the case.

Therefore, scientists diligently searched for another, simpler way to determine longitude. The idea of ​​this method was obvious - it was necessary to create a watch with the help of which the time of the reference meridian could be carried with you on a ship.

Clocks with a pendulum were unsuitable for this purpose; they did not tolerate pitching.

In 1714, the English Parliament passed a bill providing for a reward for a person or group of people who could determine longitude at sea. A reward of £10,000 was offered if the method could determine longitude to within one degree of the great circumference, or sixty geographical miles. If the accuracy doubled, the amount doubled and amounted to 20 thousand pounds sterling. It was truly a royal prize!

This prize, although not entirely, went to the inventor of the chronometer, London watchmaker John Harrison. His first chronometer was made in 1735, then for several decades Harrison improved his brainchild.

With the advent of the chronometer, the problem of transporting accurate time was solved.

When setting sail, the ship's navigator checked his chronometers, and there were usually several of them, with the observatory clock, the longitude of which was well known. The local time and latitude of the ship were determined using a sextant from the Sun or the stars.

This method of determining coordinates made it possible to find the position of the ship with an accuracy of seconds, which was a distance of about 1 km at the equator.

Such accuracy suited sailors quite well on the open sea, but was insufficient near the coast, and here lighthouses equipped with light and sound signals came to their aid.

In the last century, an urgent need arose for precise coordinates on the Earth's surface. This was mainly due to the compilation of maps. The principle of determining exact coordinates was the same as at sea, but instead of a sextant, a universal instrument and a theodolite were used - instruments that made it possible to determine latitude and local time from observations of stars with great accuracy. The main difficulty, as before, was the problem of storing Greenwich time. Even good chronometers, without control, quickly moved ahead or fell behind, and an error of, say, one second of time in determining longitude was completely unsuitable for precise geodetic work.

A real revolution in determining coordinates was made by the invention of the telegraph, and then the radio. Now exact time signals from Greenwich, or from a point with a known longitude, could be received anywhere on Earth. Everything depended on the power of the transmitter and the sensitivity of the receiver.

The problem of determining longitude was solved for many decades.

However, this problem still had one weak point - astronomy.

It is not always possible to make astronomical observations; they require special skills, they are very inconvenient to make from an airplane, from a rocking ship, and on Earth, without stationary pillars, it is also impossible to get good results.

In the second half of our century arose fundamentally new idea determining coordinates on the Earth's surface. The essence of this idea is this.

Three radio stations transmit precise time signals at the same physical moment. Let's say, for example, that these stations are located on different continents. One in Europe and two in North and South America. Then, the ship's navigator, receiving these signals on his watch, which is synchronized with the clocks of the supply stations, finds the time delays of the signals t 1, t 2, t 3, i.e., the times during which the radio wave must travel from the station transmitters to the receiver. Then multiplying the t values ​​by the speed of light, the navigator finds the distance l 1, l 2, l 3 from all three stations. Drawing circles on the map around the station with radii l 1, l 2, l 3, the navigator determines his place on the map at their intersection. This is just a principle. In reality, the matter is much more complicated. It is necessary to take into account the curvature of the Earth, features in the speed of propagation of radio waves, errors in receiving equipment, and much more. It is especially difficult to synchronize a ship's clock and maintain this synchronization over a certain period of time.

However, with the advent of computers and atomic standards that store time with the stability of a second with an accuracy of 10 -12 s, all these problems were resolved. If the accuracy of clock synchronization and signal reception errors were 3-5 microseconds, then the on-board computer could determine the position of a ship or aircraft with an error of about 1 km. Moreover, this data, if available large number special radio stations could be issued continuously.

Systems such as the American Laurent and the Soviet RNS have completely solved navigation problems with an accuracy of several hundred meters.

A great contribution to the problem of determining coordinates was made by artificial satellites Earth. If a satellite is equipped with an atomic frequency standard, it can perform the tasks of a transmitting station. The advantages are obvious - the influence of the atmosphere when receiving signals from a satellite is minimal, reception errors are small.

There are also difficulties - the satellite is mobile, and therefore its coordinates are constantly changing. But these difficulties can be overcome.

The satellite’s on-board computer stores data about its trajectory, that is, its coordinates, which it continuously transmits along with time signals in a special code. The code is needed so that it is known from which satellite the information is coming.

Any consumer of these signals, receiving them on his watch, determines the time delay t and, therefore, the distance to the satellite, at some moment equal to l=tc, where c is the speed of radio waves. That is, the principle is the same as in the Laurent system, but there are improvements. The consumer clock synchronization error is considered as an unknown quantity, therefore it is determined not by l=tc, but by l 1 =t+t 1 c, where t 1 is the consumer clock synchronization error. The value l 1 is called pseudorange. If you receive signals from not one, but from four or more navigation satellites, you can obtain a system of equations from which the coordinates of the observation location and, separately, the synchronization error of the local clock are determined on a computer. Considering that the stability of modern atomic clocks has increased sharply (the stability of the second is now about 5 * 10 -14), it is possible to obtain the position on the earth's surface with the help of navigation satellites with an accuracy of several meters, and this is not the limit. Special, more advanced equipment allows us to talk about centimeter accuracy. And finally, the last question - where to get satellite coordinates? This requires special trajectory measurements, as well as a center for processing them. In the USA there is a GPS radio navigation system, we also have such a system in Russia, it is called GLONASS.

This system should consist of 24 satellites located in different orbits so that at least four satellites are visible from each location on the earth's surface served by the system.

The position of each point on the earth's surface is determined by its coordinates: latitude and longitude (Fig. 3).

Latitude is the angle formed by a plumb line passing through given point on the surface of the Earth, and the plane of the equator (in Fig. 3 for point M angle MOS).

No matter where the observer is on the globe, his force of gravity will always be directed towards the center of the Earth. This direction is called plumb or vertical.

Latitude is measured by the arc of the meridian from the equator to the parallel of a given point in the range from 0 to 90° and is designated by the letter f. Thus, the geographic parallel eabq is the locus of points that have the same latitude.

Depending on which hemisphere the point is located in, the latitude is given the name northern (N) or southern (S).

Longitude called dihedral angle between the planes of the prime meridian and the meridian of a given point (in Fig. 3 for point M angle AOS). Longitude is measured by the smaller of the arcs of the equator between the prime meridian and the meridian of a given point in the range from 0 to 180° and is designated by the letter l. Thus, the geographic meridian PN MCPs is the locus of points having the same longitude.

Depending on which hemisphere the point is located in, the longitude is called eastern (O st) or western (W).

Latitude difference and longitude difference

During navigation, the ship continuously changes its place on the surface of the Earth, therefore, its coordinates also change. The magnitude of the change in latitude Af, resulting from the passage of a ship from the departure point MI to the arrival point C1, is called difference in latitude(RS). RS is measured by the meridian arc between the parallels of departure and arrival points M1C1 (Fig. 4).

Rice. 4

The name of the RS depends on the location of the parallel of the arrival point relative to the parallel of the departure point. If the parallel of the arrival point is located north of the parallel of the departure point, then the RS is considered to be made to N, and if it is to the south, then to S.

The magnitude of the change in longitude Al resulting from the passage of a ship from the departure point M1 to the arrival point C2 is called longitude difference(RD). The taxiway is measured by the smaller arc of the equator between the meridians of the point of departure and the point of arrival MCN (see Fig. 4). If, during the passage of the vessel, the eastern longitude increases or the western one decreases, then the taxiway is considered to be made to O st, and if the eastern longitude decreases or the western longitude increases, then to W. To determine the taxiway and taxiway, the formulas are used:

РШ = φ1 - φ2; (1)

RD = λ1 - λ2 (2)

Where φ1 is the latitude of the departure point;

φ2 - latitude of arrival point;

λ1 - longitude of departure point;

λ2 - longitude of the point of arrival.

Wherein northern latitudes and eastern longitudes are considered positive and are assigned a plus sign, while southern latitudes and western longitudes are considered negative and are assigned a minus sign. When solving problems using formulas (1) and (2), in the case of positive RS results, it will be done to N, and RD - to O st (see example 1), and in the case of negative RS results, it will be made to S, and RD - to W (see example 2). If a RD result is more than 180° with a negative sign, you need to add 360° (see example 3), and if the RD result is more than 180° with a positive sign, you need to subtract 360° (see example 4).

Example 1. Known: φ1 = 62°49" N; λ1 = 34°49" O st ; φ2 = 72°50"N; λ2 = 80°56" O st .

Find RS and RD.

Solution.

Example 2. Known: φ1 = 72°50" N; λ1 = :80°56"O st: φ2 = 62 O st 49"N;

Find RS and RD.