Time is local, zone, solar. How to determine local time How to calculate standard time

Conversations on the topic of summer, winter, zone, local, astronomical time inspired me to this post. I'll tell you and show you how to calculate local time. You will learn what standard time is. There will be some theory and history here. And there will be no medicine and physiology, and I will also leave aside political and economic views on this issue. I am not a doctor, not an economist, and even more so not a politician, I am a navigator.
Therefore, one of the sciences necessary for navigation even in our time - nautical astronomy is well known to me.
Nautical astronomy allows you to control the position of the ship according to the observations of celestial bodies. The heavenly bodies are constantly moving, and in order to determine their place at a given moment, it is necessary to know the laws of their motion, studied in astronomy. The same applies to artificial earth satellites. Nautical astronomy, in addition, provides information about the service of time and various phenomena occurring on Earth (sunrises / sunsets, illumination, eclipses, etc.) and in the Universe.
The main tasks solved by nautical astronomy are:
- determination of the place in the sea according to the observations of the luminaries;
- determination of corrections of direction devices (compasses);
- provision of time service.
Auxiliary tasks:
- definition of illumination;
- climaxes of the luminaries, etc.

Now we come to the topic of time. It is clear that humanity has taken one day as a unit of time - during this time the Earth makes one revolution around its axis, or a period of time from sunrise to sunrise. Then this period of time was divided by 24 and received - 1 hour. Since one revolution is 360 degrees, we get that 1 hour is 15 degrees of the Earth's rotation around its axis (the apparent movement of the Sun), and one degree of the Sun's movement (the Earth's rotation) is 4 minutes of the time accepted by earthlings.
And let's not complicate the task with the knowledge that:
- the rotation of the Earth slows down by 0.00023 seconds per century;
- random abrupt changes in the speed of the Earth's rotation (several of them were noted, one - in 1920 by 0.000000045 s);
- the value of the true solar day during the year varies by an average of 59.14 s;
- a year is not 365 days, but 365.2422 days.

Therefore - to discuss the topic of sleep-rest-work and change the clock, we will not talk about the true solar and sidereal times (astronomical). We will only operate with the average solar time, accepted for time calculation on Earth. When the length of the day is calculated not from one day, but on average for 1 year.
The local time - time of the observer on the given meridian, and since there are countless meridians, then there are countless local times. But all observers on the same meridian have the same local time.
Greenwich time is the local time of an observer standing on the Greenwich meridian.
Because The Greenwich meridian is taken as the origin of longitude on the globe, then local time differs from Greenwich by exactly the longitude of the place, converted from angular measure to time based on 360 degrees = 24 hours.
There is a saying:
"Longitude west, Greenwich time best.
Longitude east, Greenwich time least".
Which in arbitrary translation means that with east longitude you have more time than Greenwich, and with west longitude you have less time than Greenwich.

Now we know that Greenwich Mean Time is taken as a reference point, but local time is inconvenient for everyday life.
Therefore, a single time was adopted for a whole region or country (of a local observatory, a ruler's palace, etc.). But...
With this approach, there are inconveniences - the difference with the time of another region or country could contain fractional parts of hours and even minutes. The development of civilization, communication between peoples required streamlining the account of time.

At the astronomical congress of 1884, a standard time system was proposed and gradually adopted in almost all countries of the world. In the standard time system, time is counted on 24 central meridians of the Earth, separated by 15 degrees of longitude, so that in neighboring zones the time differs by 1 hour. Standard time extends over 7.5 degrees of longitude on either side of the central meridians.
standard time Standard time is the average local time of the central meridian of a given time zone, adopted throughout the zone.

But there is a small focus - on the 12th central meridian, the longitude is 180 degrees, and one part of its belt is in the eastern hemisphere, and the second is in the western. The time on the clock of the inhabitants of this zone is the same, but the number on the calendar of the inhabitants of the eastern and western hemispheres is different and differs by 1 day. The inhabitants of the Western Hemisphere still have yesterday, in comparison with us - the inhabitants of the eastern part of the Earth. And the meridian is called the international date line.

With such a structure of zones, standard time cannot differ from local time by more than 30 minutes. However, the theoretical boundaries of the belts are respected only in the seas, oceans and sparsely populated areas. In fact, the boundaries of the belts are determined by the governments of countries, taking into account administrative, geographical and economic features.

Decree time. In order to save electricity in the evening lighting, clocks in the USSR were set 1 hour ahead of standard time. Initially, this time was introduced only in the summer (summer time), but by decree in 1931 it was left permanently. That is, standard time is standard time 1 hour.

Summer time. In a number of countries, the clock is moved forward 1 hour (sometimes 2 hours) only for the summer. In the USSR, summer time (1 hour to maternity time or 2 hours to standard time) was introduced in 1980. I will not describe the further game with time and time zones in our country - everyone knows.
Today, our country is divided into time zones in this way.

The resulting longitude (in order not to waste time on trifles, we take only an integer number of degrees) is translated into hours and minutes at the rate of 15 degrees - 1 hour, 1 degree - 4 minutes. We make a small assumption that the Sun passes its upper climax (noon) around 12:00 local time (in fact, 12:00 plus or minus about 15 minutes).
Now from 12:00 we subtract (for the eastern hemisphere, and for the western hemisphere we add) the obtained value of longitude in hours and minutes. We get the Greenwich time of half a day at a given meridian (longitude). Next - add the difference on your clock with Greenwich (UTC, universal) time for the eastern hemisphere (and subtract if we consider the western hemisphere).
Ask: "Where can I find Greenwich Mean Time?" I will answer - this is today's Moscow minus 4 hours (today is February 3, 2013, otherwise we don’t know what will happen with time tomorrow).

Example: east longitude 33 degrees, Moscow time, i.e. Greenwich 4 hours

Convert longitude to hours:
- 33/15=2.2 means 2 hours
- 2,2-2=0,2
- 0.2*60=12 means 12 minutes
- longitude 33 degrees expressed in hours - 2 h 12 m.

Determine the time of our local GMT noon:
12h00m - 2h12m = 9h48m

Add the difference of hours (what is on the hand or next to it) with Greenwich Mean Time:
9h48m + 4h = 13h 48m.
This is the time of half a day according to our watch (which is on the hand or nearby) in a place with a longitude of 33 degrees of the Eastern Hemisphere (remember - with an accuracy of 30 minutes, because the Sun is not always at 12.00 at its upper climax). For an accurate calculation, navigators use astronomical tables.

Now standard time. It is necessary to convert the longitude of the place into hours and round up to the nearest hour.
For example: longitude 142.9 degrees East.
142,9/15=9,526
So the 10th eastern time zone. Those. 10 hours ahead of Greenwich.

A few words about the sunrise. At the Equator, the Sun always rises around 6 am local time, respectively, sets around 6 pm. Further to the North or South, the time of sunrise and sunset depends on the latitude of the place and the time of year. But on the days of the spring and autumn equinoxes at all latitudes, the Sun rises and sets, as on the Equator - around 6 and 18 hours local time.
On the example of St. Petersburg and all places at a latitude of 60 degrees north latitude. local time:
March 20 Sunrise at 6:00 Sunset at 18:15
June 21, sunrise at 2:36 a.m., sunset at 21:28 p.m.
September 22, sunrise at 5:45 a.m., sunset at 6:00 p.m.
December 21 sunrise at 8:50 a.m., sunset at 2:55 p.m.

Used by: "Nautical Astronomy" B.I. Krasavtsev (Moscow "Transport" 1986), MAE 2012.

When solving many problems of aviation astronomy, it is necessary to know the local time, which underlies all astronomical observations.

Local time is the time at a given geographic meridian (the meridian of the observer). Each meridian has its own local time. It can be stellar, true solar, and mean solar. All these times have some common features. Consider them in relation to local mean solar time, which is counted from the meridian of midnight.

On fig. 3.9 point O represents the North Pole of the Earth, straight line OA is the meridian of midnight, and straight lines OB and OS are the geographical meridians of points B and C of the earth's surface, having geographical longitudes and Local mean solar time on the indicated meridians at the same moment is indicated by . Directly from the figure under consideration, it is possible to establish the features of local time:

Rice. 3.9. local mean solar time

on the entire geographic meridian, local time is the same at the same moment;

to the east of any meridian, local time increases, and to the west it decreases;

the difference in local times on two meridians at the same moment is always equal to the difference in the longitudes of these meridians, expressed in units of time, i.e. . This ratio is widely used in solving practical problems of aviation astronomy. It allows you to determine the local time at a given point from the known time of another point. It is inconvenient to use local mean solar time in everyday life, since even in different areas of one large city it differs by some amount, and therefore it is very difficult to link it in everyday life, transport and communications.

Relationship between time and longitude.

It was established above that local time is closely related to the longitude of a place. Consequently, there is a certain relationship between time and longitude of a place, which can be established on the basis of the daily rotation of the Earth. During the day, the Earth makes a complete rotation of 360 ° relative to that point in the celestial sphere, according to which time is determined. Based on this, we can derive the following relationship between time and longitude of a place: .

This relationship is valid for both solar and sidereal time, i.e., for any system of time measurement. It allows the longitude of a place to be expressed in time and, conversely, time to be expressed in units of an arc and greatly simplifies the solution of many practical problems of aviation astronomy.

Example 1. Convert longitude to time.

Solution. Knowing that 15° correspond to , we determine an integer number of hours. and in the remainder;

we translate the received remainder of degrees during: min; we translate the minutes of the arc into time: . Finally we get:

Example 2. Convert longitude in time to arc units.

Solution. Knowing that corresponds to min correspond to correspond, we translate:

whole hours to units of arc: minutes of time to units of arc. seconds of time to units of arc. .

Finally we get:

Determination of local time at a given point.

In the practice of aviation astronomy, the method of determining the local time at a given point from the known time of another point is widely used. Local time at a given point is determined by the formula

where is the known local time at one point; - the desired local time at a given point; - the difference in longitudes of these points, expressed in time.

The time calculator is needed in order to find out what time it will be in the place you need.

For example, you want to call your beloved grandfather in Vladivostok to wish him a happy birthday. You know that the guests will sit at the festive table at half past seven in the evening, and you want to congratulate him at that very moment.

But you yourself, by coincidence, are in the city of Darwin, Australia, and you need to find out at what time, Australian time, the birthday celebration will begin.

This is where our calculator comes in handy. To find out the time, you just need to indicate half past seven and the date of your birthday in the left column, select Vladivostok in the same place and click on the "=" button between the columns

How to use the time calculator?

On the calculator panel you can see two columns - a source and result

A source is the date, time and place known to you. Result- the desired date and time.

You can set the time and date in the source by simply clicking on the corresponding field with the mouse.

After setting the date and time, you need to specify the location for which you set the time. In the happy birthday example, this will be the city of Vladivostok.

Below the fields for setting the date and time is the item time is set to is a switch. With it, you can specify whether you specified the time for a specific city or for a time zone. To find out the time of Vladivostok from our example, you can select both the city itself and the time zone of Vladivostok - VLAT.

To switch from specifying a city to specifying a time zone, simply left-click on the switch.

Name is the name of the object for which the time has been set. Based on the value of the switch, it can be the name of the city or the name of the time zone.

After setting the date, time, and location of the source, you need to specify which location you are looking for the time for. In our happy birthday example, it's Darwin, Australia. With a similar switch, you can also specify both the city itself and its time zone - ACST

After setting all the values, just click on the " = "between the fields, and find out the time you are looking for!

All buttons of our calculator are signed, and if you forgot the meaning of a particular button, hover over it with the mouse. After a second, a tooltip with its value will appear.

How to determine local time. As you already know from the 7th grade geography course, at the same moment at different points on the planet, lying on different meridians, there will be different local (Those. solar )time . You know that this is due to the rotation of the Earth around its axis. The same time will be only at all points lying on the same meridian. So, on the western and eastern outskirts of even one settlement, local time will be different. This difference will increase with increasing distance between the meridians. So, on neighboring meridians drawn through 15 °, the difference in local time is 1 hour, Drawn through 1 - 4 hv, Drawn through 1 "(one minute, one degree divided by 60 minutes) - 4 s (it is at such angular distances that the points rotate one meridian for the specified time intervals).

At the same time, local time on the meridian, located to the east of which point, is ahead of the time in it, and on the more western meridian - to lag behind. For example, if local time in Kiev afternoon snack (12 h), then in Donetsk it's already 12:29, A at Lviv at this moment - only 11 hours 33 minutes 56 seconds. Therefore, in order to establish the exact time at different points, knowing it at one of them, it is necessary to carry out such calculations.

a) Kiev - 30 ° 34 "E;

b) Donetsk - 37 ° 49 "E;

c) Lviv - 24 ° 03 "E.

2. Set the difference in longitude between points (in degrees and minutes):

a) between Donetsk and Kiev - 37 ° 49 "- 30 ° 34" = 7 ° 15 "E;

b) between Kiev and Lvov - 30 ° 34 "- 24 ° 03" = 6 ° 31 "East.

3. Convert longitude difference (from degrees and minutes) to time difference (in hours, minutes and seconds):

a) 7 ° 15 " = 7 x 4 xv15 x 4 s = 29 xv;

b) 6 ° 31 "= 6 x 4 xv 31 x 4 s = 26 xv 4 s.

the values ​​found show the difference in local time on the meridians drawn through Kiev, Lvov and Donetsk.

4. Until the time known to us in Kiev (12 hours) Add (in the case of Donetsk, which lies to the east of Kiev) or subtract from it (in the case of Lvov, which is located to the west of Kiev) the resulting value:

a) if it is 12:00 in Kiev, then the local time in Donetsk will be

12 h + 29 hv = 12 h 29 hv;

b) if it is 12 o'clock in Kyiv, then the local time in Lviv will be

12 h - 26 hv 4 s = 11 h 33 hv 56 s.

Time zones and standard time. It is almost impossible to use local time, which is different in every point, in everyday life. For convenience all over the world enjoy standard time . For this, as you know, the globe was conditionally divided by meridians into 24 bands (by the number of hours in a day) - into Time Zones(At 15° longitude each). At all points of one zone, we agreed to consider the time the same. According to standard time, the local time of the meridian passing through the middle of this belt (middle meridian) is taken.

Time zones are numbered from 0 to 23 in the east direction: the middle meridian of the 0th zone is Greenwich(Starting) meridian, 1st belt - meridian 15 ° east. d., 12th belt - 180th meridian, 23rd belt - meridian 15 ° W. d.

The time of the 0th belt is called Western European , 1st - Central European , another - Eastern European . The zone number indicates the standard time at the moment when the north is on the Greenwich meridian. The time difference between two neighboring zones is 1 hour. Moving around the globe from west to east, we must move the clock forward one hour when crossing the boundaries of each next zone, and moving westward - one hour back.

The location of Ukraine in relation to time zones is convenient: 95% of its territory lies in the second zone, only Luhansk and parts Donetsk and Kharkov regions- In the 3rd belt, and a small part Transcarpathian region- in the first belt. However, in practice, for convenience, the boundaries of time zones on land are drawn not strictly along the meridians, but taking into account state borders. Therefore, the entire territory of Ukraine is assigned to the second time zone. Standard time in our country is the average time for the second meridian zone (30, which passes almost through Kiev. Therefore, in Ukraine, the belt is also called Kiev .

Amazing Ukraine

By the time of the second belt, in addition to Ukraine, Belarus, Latvia, Lithuania, Estonia, Finland, Moldova, Romania, and Turkey also live in Europe. All the western neighbors of Ukraine, the countries of Central and most of the countries of Western Europe use Central European time, while Great Britain, Ireland, Iceland and Portugal use Western European time. On the Russian territories adjacent to the borders of Ukraine, the so-called Moscow time operates, which is ahead of Moscow by 1 hour

Ri c . Time zones of the world

Summer time. Every year Ukraine introduces summer time : on the night of the last Sunday in March, the hour hand is moved forward one hour. This makes it possible to make better use of the light part of the day and save electricity. On the night of the last Sunday in October, the clock is returned an hour back, restoring the standard time.

The introduction and abolition of summer time is carried out synchronously by most European

From the book by A.A. Gurshtein "Eternal secrets of the sky"

EVERYONE HAVE TIME

The picture of the daily visible movement of the Sun across the sky is already familiar and understandable to us. The sun rises, rises above the horizon, reaches the upper climax, descends and sets. The calculation of time within a day for all peoples has always been associated with this apparent movement of our main luminary. The sun rises - morning comes in this place, the Sun tends to the horizon - evening approaches in this place.The moment of the upper climax of the Sun is the true middle of the day. We call this moment local noon .
This pattern is observed anywhere in the world. (The exception is the areas adjacent to the North and South Poles of the Earth; the essence of the apparent movement of the Sun across the sky there remains exactly the same as in any other place, but outwardly the picture looks somewhat different - in these areas, the summer polar day and winter polar night alternate In order not to unnecessarily complicate the explanation, we will not touch on these features in what follows).
Wherever you are in the middle latitudes - in Moscow, in Khabarovsk or, for example, in Rio de Janeiro, everywhere the Sun will sooner or later reach its highest height in its daily movement. Such a moment would mark the true middle of the day. For a given point on the globe, this will be local noon.

But now let us look back at our Earth from the depths of interplanetary space. We will immediately discover that noon occurs in different places on the Earth by no means at the same moment in time. One half of the planet is illuminated by the Sun, but on the other half of the globe the Sun is not visible at all - night reigns there. On the illuminated half of the Earth, the time of day is also different in different places. Near one edge, where the Sun has just risen, morning has recently come. And near the opposite border of the illuminated and dark parts of the Earth, the Sun is about to disappear - they are already preparing for the arrival of the night.
An important conclusion suggests itself: clocks running according to local time, which can be determined both by the movement of the Sun and by the movement of stars, simultaneously show different times in different parts of the globe. Local time depends on the location of the observation point on the earth's surface.
Consider now such a geometric scheme. As is well known, it is always possible to draw a plane through three points, and moreover, only one. Imagine a plane passing through both poles of the Earth, North and South, and through the center of the Sun. Our "solar" plane will cut the surface of the Earth in a circle. Since both poles of the Earth lie in the plane under consideration, the axis of rotation of the Earth also lies in it, and therefore, the circle along which our plane cuts the surface of the Earth is nothing more than the plane of one of the meridians. This meridian runs just in the middle of the half of the Earth illuminated by the Sun. Only on this meridian - and nowhere else - has it now been local time for true noon.
Of course, in different parts of this meridian, the height of the Sun above the horizon at the moment we are considering is different. But it is essential that at each point of our meridian the Sun culminates. It rose to the greatest height for each of the points of this meridian. Here the moment of the upper culmination of the Sun has come everywhere - the middle of the day, the local noon. So we have established that local time does not depend on the latitude of the place of observation. It is the same on the same meridian and changes only depending on longitude, when moving from meridian to meridian.
The axis of rotation of the Earth constantly remains in the "solar" plane chosen by us. And the Earth continues to rotate around its axis. And new and new meridians continuously fall into our "solar" plane. And no matter what meridian now turns towards the Sun, it is at this moment that the local noon comes on it.
The earth will make a full rotation around its axis by 360 ° in a day, in 24 hours. During the same time, the local noon "bypasses" the entire surface of the Earth. From here it is easy to calculate with what speed the local noon "moves" from the meridian to the meridian.
In one hour, the Earth will rotate 15°. Thus, if two points lie on meridians exactly 15° apart, then the difference in local time will be exactly 1 hour for them. The angle between the meridians, as we have already said, is the difference in longitude. And if we learn to determine the difference between the local times of two points, then by doing so we will learn to determine the difference in their longitudes.
This is exactly what astronomers do. They determine the differences in local times of given points at the same physical instants of time and convert the differences in times into differences in longitude. Astronomers have become so accustomed to these translations that they have learned to count angles in the usual way, in degrees, and in hours. Here's how it works: 24 hours - 360 degrees, 1 hour - 15 degrees.
Further, one must be careful, since the names "minute" and "second" refer to both fractions of an hour and fractions of a degree. Therefore, in order to avoid confusion, it is necessary to indicate "minute of time" or "minute of arc", "second of time" or "second of arc":
1 minute of time (1t) = 15 minutes of arc (15");
1 second of time (18) = 15 seconds of arc (15").
The astronomer will not be at all surprised if he reads that the difference between the longitudes of Moscow and London is about 2 hours and 28 minutes. This is equivalent to what to write: the difference between the longitudes of Moscow and London is about 37 °.
(We still simplify the explanation and do not take into account the situation at the poles; during the period of the polar day, on a small segment of the meridian near the pole, the Sun in the position we have described may not be in the upper. but in the lower climax. Such a moment is formally true midnight, although The sun never sets below the horizon.
So, local time is the same only on the same meridian. And on any line of equal latitudes - parallels - each point has its own time. But it is completely unacceptable to use one's own time for practical life at every point on the Earth.
As long as people traveled on the surface of the Earth in horse-drawn stagecoaches or in slow-moving ships, the inconveniences of use at various times were not too striking. After all, every city and every port had the luxury of having its own time. But with the development of cultural and economic ties, especially with the start of the construction of long railway lines, the situation deteriorated sharply. Travelers were confused, mail was confused, railway timetables were confused.
The idea arose to regulate the work of industry and the movement of transport according to the time of the capital. And in general, to build the entire life of the country according to a single time. But even this turned out to be almost impossible. In a country as long in longitude as, for example, Russia, the time difference between the cities of the Far East, Siberia and the European part of the country reaches many hours. What would happen if a clock somewhere in Khabarovsk showed midnight, but in fact it was morning there a long time ago? No, the common time for large countries, too, obviously, was not good.

A witty way out was proposed in the second half of the last century by the Canadian railway engineer Fleming. He invented the so-called standard time. Fleming's idea found wide support, and standard time is now used throughout the globe.
The surface of the Earth is divided along the meridians into 24 belts: the width of each of them is approximately equal to 15 ° in longitude. Within each zone, time is considered common, and from zone to zone it differs by exactly one hour. Thus, the minute and second hands of clocks throughout the globe must show exactly the same thing; only the hour hands differ.
In the USSR, standard time was introduced in 1919 by a decree of the Council of People's Commissars "in order to establish a time counting that is uniform with the entire civilized world during the day, causing the same clock readings in minutes and seconds throughout the globe and greatly simplifying the registration of the relationship of peoples , social events and most natural phenomena in time".
For convenience, the boundaries of time zones are not drawn strictly along the meridians, but are combined with the borders of states, administrative borders, water lines, and mountain ranges.
In the middle of the zero time zone passesGreenwich meridian. It was adopted as the initial reference meridian for the globe at an astronomical conference in Washington in 1884. The zero belt should live according to Greenwich Mean Time.

Western Europe falls into the first time zone. The time of this zone is called Central European. But, as we agreed, the boundaries of time zones are very conditional. In 1968, the British government, in order to emphasize the common interests of England and Europe, abandoned Greenwich time and introduced Central European time in the country.
The European part of the USSR lives according to Moscow time - this is the name of the time of the second time zone. But one should not lose sight of the fact that Moscow time differs from Central European time not by one hour, but by two. This is due to the fact that from June 16, 1930, the so-called maternity time was introduced on the territory of the USSR (excluding the Tatar ASSR). By decree of the Council of People's Commissars, standard time in our country was increased by exactly one hour. The introduction of daylight savings contributed to energy savings.
Daylight savings time is used in many countries. Often it is introduced by decree only for the summer period. Then they say about it - "summer time". And in winter, the country again switches to normal standard time. Such a system existed in France, England, Switzerland and other countries. Temporary translation of the hands one hour ahead was also practiced in our country. "Daylight Saving Time" was used between April 20 and September 20. However, in the fall of 1930, the reverse transfer of the hands from "summer time" to "winter time" did not happen. Our country began to live permanently according to the decree time.
Other countries are also switching to year-round use of maternity time. Since 1940 it has been introduced in France, since 1968 in England.
On the territory of the USSR there are time zones from the second to the twelfth. In connection with the growth of the economy and the new territorial division of the country, the boundaries of time zones are updated from time to time. So, they were slightly changed in 1956.
Along the state border of the USSR in the Bering Strait, between Cape Uelen and Alaska, passesinternational date line.
The question of changing dates, of the arrival of a new day on Earth, had not had a clear solution for many centuries.
For the first time, the great “disturbance of the minds” due to the calculation of time arose in the 16th century. in connection with the completion of the circumnavigation of the Victoria, the only one of the 5 caravels of Fernand Magellan.
In 1522, after 3 years of wandering, 18 survivors of Magellan's expedition reached the Cape Verde Islands. And here Antonio Pigafetta, a diligent chronicler of the voyage, discovers a mysterious loss. From year to year, he and helmsman Alvo independently kept count of the days on the ship. The possibility of miscalculation was completely excluded. However, it is Wednesday on the Victoria, although it is already Thursday in Europe. The joy of returning to their native shores turns into unexpected grief for the sailors. They "mistaken" in the count of days and, consequently, confused all church holidays. Having circumnavigated the globe from east to west, Magellan's satellites "lost" exactly one day.
A similar situation was subsequently used Jules Verne . The action of the novel "Around the World in 80 Days" reaches its maximum tension. The main character, the Reform Club original Phileas Fogg, Esq., returns to London five minutes late. He is sure that he lost the bet, and dejected goes home. But he forgot that he was driving from west to east, towards the rising sun. Every day he met the sunrise a few minutes earlier than if he had remained in place, and as a result, Fogg brought Saturday with him, although it was still Friday in London. The novel has a happy ending.
Astronomers not only divided the Earth into time zones, but also established a strict international date line. It passes through the Pacific Ocean between the twelfth and thirteenth time zones. This limit is, of course, conditional. But according to an international agreement, this is where a new day begins. Only here and nowhere else on the globe can you take one step and move from today to yesterday.

TIME IS DRIVED IN A CARRIAGE

The idea of ​​the geographic longitude of points on the earth's surface, along with the concept of geographic latitude, has come into use since ancient times. However, the latitude was calculated from astronomical observations relatively simply. Eratosthenes already knew how to determine the difference in latitudes. With the definition of longitude for many centuries, things were very bad.
Only from astronomical measurements, without involving any additional information, longitude was not able to be determined either in ancient antiquity or in the Middle Ages. This circumstance is connected, in particular,Christopher Columbus' Greatest Delusion.
Preparing to cross the "Sea of ​​Darkness" and reach the shores of India by the western route, Columbus assumed the radius of the Earth to be much shorter than in reality. Columbus used a very precise Arabic measurement of the radius of the Earth, expressed in miles. But he did not take into account that the modern mile was 20% shorter than the one used by the Arabs six and a half centuries before him. Calculating the range of the upcoming voyage, Columbus thereby greatly "shortened" his path. And, having reached the Bahamas in October 1492, he was deeply convinced that he was already near the shores of the Asian continent. No wonder Columbus called the newly discovered lands the West Indies - the Western Indies. This name, along with the name of the native inhabitants of America, who for the same reasons were dubbed Indians, has survived in geographical literature to this day.
Columbus' delusion did not dissipate until the end of his life. Having organized four expeditions to the shores of America, he was still convinced that he was sailing somewhere near the tip of Asia.
The ignorance of the great navigator depended entirely on the errors of medieval maps and the inability to accurately determine geographic longitude. Latitude could be calculated by him from astronomical observations. And longitude was estimated primarily by the path traveled by the ship. But since the radius of the Earth was taken by Columbus to be greatly reduced, the calculated longitudes did not correspond to the truth at all.

If Columbus had been able to perform a determination of geographic longitude independent of the map and side navigational considerations, he would have immediately established that he had sailed not so far from the coast of Europe. In his voyages, he never went beyond 85 ° west longitude.
As we have already found out, geographical longitude is determined astronomically as the difference between the local time of a given point and the local time of the initial, taken as zero, meridian. To determine longitude, one should observe any astronomical phenomena that occur almost simultaneously over vast areas of the earth's surface.
It is done like this. Astronomers working on the zero meridian, using long-term series of observations, predict the moments at which the desired phenomenon occurs according to the local time of the zero meridian. These predictions are published in special tables. In the future, the astronomer-navigator or astronomer-traveler establishes from his measurements the moment of local time when the expected phenomenon occurred at the observation point. The result is compared with the table data.
Since the phenomenon selected for observation must occur simultaneously for all parts of the Earth, the difference between the local time at the observation point and the local time indicated in the table for the zero meridian strictly corresponds to the difference in longitude.
For the purpose of determining longitudes by the method described, for example, lunar eclipses are more or less suitable. They are observed on that half of the globe where the Moon is visible during this period. But lunar eclipses are too rare. They would have to wait months. And for the needs, for example, of the same navigation, it was necessary to find phenomena that would happen as often as possible, preferably even every day.
Galilee th, who discovered 4 bright satellites of Jupiter in a telescope, proposed using these particular luminaries to determine the longitudes of the eclipse. When a satellite goes beyond the edge of Jupiter or goes into the shadow of the planet, it disappears from sight, "goes out." Eclipses of the moons of Jupiter occur frequently, almost several times a day.
Galileo's proposal was seriously interested States General of Holland. They held special negotiations with Galileo on this issue. But this method did not immediately find application due to the low quality of the originally compiled tables.
Both lunar eclipses, and eclipses of the satellites of Jupiter, and observations of the movement of the Moon among the stars provided astronomers with a means of determining longitudes. But scientists did not retreat in search of even more reliable and accurate methods. They saw the most promising way to solve the problem in the "transportation" of time.
Let's assume that you are on the prime meridian. Here, in the observatory, it is possible to set the clock exactly according to the local time of the prime meridian. Then you go on a long journey, and your watch continues to show the local time of the prime meridian. When you reach your destination, you perform an astronomical determination of the local time. Comparing the result with the clock reading immediately gives you the longitude value.
This method is very simple and elegant, as long as your watch can reliably store the time of the prime meridian. Errors in the readings of the clock have a very noticeable effect on the accuracy of determining longitudes. So, if you are moving along the equator, an error in time of only 1 minute leads to an inaccuracy in determining the location on the surface of the Earth by almost 30 km. And if, unfortunately, due to a storm or from the heat, during the long months of sailing, your watch either lags behind, or runs ahead, say, by an hour, then the error in determining the longitude will already be 15 °. This means that the error in determining your position on the surface of the Earth will exceed 1500 km.

So, To accurately determine longitudes, first-class watches are needed - the keepers of the exact time.
Of course, clocks have been at the disposal of astronomers since ancient times. First, it was a sundial. They were installed in the squares, in places of public meetings, in the possessions of rich aristocrats. But sundials, no matter how accurate they are, always follow local time. Of course, it is impossible to transport time from one place to another with the help of a sundial.
Secondly, the ancient astronomers had a water clock at their disposal. Water clock - clepsydra- existed in Babylon, and in China, and in Greece. They were several vessels of water placed one above the other. Drops of water flowed from the upper vessels to the lower ones. But the rate of outflow of water, as it is not difficult to figure out, depends on the amount of water remaining in the vessel. The theory of water clocks was very complex, and it was not possible to achieve great accuracy from them. And it was absolutely impossible to transport them anywhere. From shaking, they immediately failed.
Finally, at the disposal of the ancients werehourglass and fire clock. The hourglass is sometimes used even now by doctors. And the fiery clock was a long rod of aromatic mixture, which was given either a spiral or some other intricate shape. The rod burned evenly, exuding incense, and the length of the burnt part of it could be judged on the elapsed time.
It is quite obvious that neither the hourglass nor the fireglass was suitable for transporting time from place to place for many months either.

To determine longitudes, astronomers needed reliable mechanical watches, which were not available at that time.
The impetus for the development of watchmaking gave Galileo Galilei, who proposed to use as a clock regulator pendulum . But the most successful solution to this problem was proposed independently of GalileoChristian Huygens. He designed a device in which the pendulum regulates the rotation of a system of gears, while itself receiving the momentum necessary to ensure that the swing of oscillation does not fade. Thus, the fundamental foundations of the most accurate measuring instrument, the mechanical watch, were laid.
As clocks improved, the conventional pendulum was replaced by a swinging pendulum. balancer . This is how the first chronometers were born. But they were still very capricious. The progress of the chronometers was strongly dependent on temperature. With a change in temperature, the dimensions of the balancer changed, and the chronometer began to either rush or lag behind. And navigators still needed accurate time.
The British Admiralty showed the greatest concern in the development of watchmaking. In the second half of the XVII century. Great Britain is increasingly moving forward on the world stage as the largest maritime power, pushing Spain and Portugal aside.
"Rule, Britannia, the seas" - this is how it is sung in the famous English song of the 18th century. English frigates ply the seas and oceans. But ship chronometers are still in need of improvement.
At the suggestion of Isaac Newton, who for a short time was an MP from the University of Cambridge, the British government established a fantastic prize for those times. For the development of a reliable method for determining longitude at sea with an accuracy of a quarter of a degree, the government promised a reward of 30 thousand pounds sterling. And the most promising here was the old way - the improvement of the chronometer.

A decisive success in this matter was achieved English watchmaker Harrison. He was the first to make a balancer from materials with different coefficients of expansion. The change in temperature was compensated by changing the shape of the balance bar. Errors in the course of the chronometer were reduced to 1 second in a whole month.
Harrison's new chronometer was put to the test in 1761 on a voyage from Portsmouth to Jamaica and back. Neither shaking, nor storms, nor high air humidity put it out of action. On his return to England, after 161 days of travel, his readings were wrong by only a few seconds.
In fairness, let's say that the promised bonus was not given to Harrison in full. After a long struggle, he received at first only 5 thousand pounds, and then with great difficulty he obtained another 10 thousand. But the task of conveying the exact time and thereby determining the longitude was brilliantly solved by Harrison.

The appearance of accurate chronometers was the first symptom of the coming technical revolution in England. The founders of machine spinning Hargreaves, Crompton, Arkwright - all studied in watchmaking workshops. It was from English watchmakers that they adopted the ability to translate their technical ideas into real, working mechanisms.
widely used to determine the longitudes of important astronomical points. A set of several chronometers was carried from point to point in carriages - this was called chronometric flight. At each point from astronomical observations, the local time was determined and compared with the readings of all chronometers. The use of several chronometers served as a guarantee against gross errors due to malfunctions of one of them, and increased the accuracy of determining longitudes.
The importance of chronometers for determining longitude declined sharply with the invention of the telegraph. An electrical signal propagates through wires at a speed of 300,000 km per second. For practical purposes of astronomy, its propagation can be considered instantaneous. The time of the zero meridian began to be transmitted to observation points by telegraph. And then the telegraph was replaced by radio. Comparing the time of the zero meridian transmitted in a special way by radio with the local time at the observation point, astronomers determine geographical longitudes with an accuracy of hundredths and thousandths of a second of time.
The problem of determining time and geographic longitudes as one of the most difficult problems of astronomy in the 17th-18th centuries. no longer exists today.
And in some places, ancient traditions have been preserved as a legacy from the past. In order to notify the townspeople of the exact time, clocks with a loud chime were previously installed on the towers, and in large cities a cannon fired exactly at noon. The melodic battle of the Kremlin chimes sounds on the radio even today. And in Leningrad, just like 200 years ago in St. Petersburg, at exactly 12 noon, a cannon fires from the Petropavlovsk kronverk.