Since time immemorial it has been known that man has 5 senses: sight, hearing, touch, smell and taste. Can we consider a sixth sense, the sense of time? How many times have we had to wake up at a certain time without having an alarm clock? The vast majority of people wake up with very good precision at the preset time even when it is not customary to get up at that time.
The measurement of time is based on the rotation of the Earth on the axis and on its translation around the sun. The calculation of time within the limits of the days in all the towns has always been linked to the apparent daily movement of the sun through the celestial vault. The sun rises and in that place the morning begins, the sun bends over the horizon and night approaches.
The time of the highest peak of the sun is the true midday, and we call this time local noon. This picture is observed in all regions of the earth except in the areas near the North and South poles, where the polar summer day and the polar winter night follow each other.
The axis of rotation of the Earth always belongs to the "solar" plane, that is, it passes through the center of the Sun. But the Earth continues to rotate around its axis and new and new meridians constantly enter the solar plane, in any of the meridians turning toward the sun will have reached local noon.
The observation made tells us that the time or local time does not depend on the latitude of the place but that the local time is the same in an entire meridian and only varies as a function of longitude when passing from one meridian to another.
The Earth makes a complete revolution around its axis that is 360 degrees after 24 hours. During that time the local noon "runs through" the entire surface of the Earth. From this it is easy to calculate how fast the local noon "moves" from one meridian to another.
In one hour the Earth rotates 15 degrees. Thus, if two points lie on two meridians exactly 15 degrees away from each other, the local time difference results for them to be an exact time.
Spending its own local time at each point on earth for practical purposes is totally inconvenient. As people moved around the world using horses or small slow-moving boats, the inconvenience of using different hours was not shocking, but with the development of cultural and economic communications, in addition to the introduction of the telegraph in 1845, when the railway, the situation sharply escalated.
The post office, the schedules of the means of transport were confused, a problem arose and, as one might suppose, it did not take long for a solution to emerge. The Canadian railway engineer Fleming proposed the selection of several special meridians to regulate the time throughout the territory of a nation. Conventionally, the Greenwich meridian was adopted as the initial meridian and from it several multiples of 15 that differ a whole number of hours from the meridian 0. The local time referred to today is in accordance with the meridian chosen in an area that extends to both sides of it.
For example: if we divide the circumference of the Earth - 360 degrees - by the time it makes a complete rotation, we will see that one hour is equivalent to 15 degrees of rotation and hence it takes 4 minutes to travel one degree of longitude.
In this way, in each time zone, all the points located at 7 degrees 30 minutes to the east and that same figure to the west of a meridian X have no time differences and instead of being governed by 15 local hours plus 4 minutes per degree, they are governed by a single legal hour. Based on this system, 24 legal hours have been established on the planet corresponding to the same number of time zones. Time zones are called the parts of the surface in which it is conventionally divided by the lines that go from its North Pole to the South Pole and that are distant from the central meridians 7 degrees 30 minutes to the east and west of it.
As we speak of conventions, the limits of the time zones only follow exactly the geographical meridians in the seas and oceans, as well as in non-populated places on the mainland, deviating when passing state borders, administrative limits, waterways, mountain ranges.
In countries that have a great extension from east to west, it is necessary to determine several time zones with their corresponding legal hours, but those that are not too long have tried to make adaptations so that a single legal hour applies throughout the territory. In the case of Russia, for example, it has 11 time zones throughout the country, that is, 11 hours of difference between its extremes, - from the second to the twelfth - however, telephone and telegraphic communications, means of land, air and transportation transport. long-distance motor vehicles are regulated according to a unified time system: Moscow time, by virtue of its conventional character.
As a small country, Cuba belongs to the time zone between the meridian 82 degrees 30 minutes to the west, plus 7 degrees 30 minutes that passes through Marianao. From this place to Cape San Antonio it would correspond to time zone 18, one hour less, but by virtue of the conventional nature of the time system to avoid this problem, the western limit of time zone 19 was deviated and there is only one hour in the entire national territory legal.
Many Western European countries left their time zone and there was then unification, all are governed by the first time zone, it is the so-called MIDDLE EUROPEAN TIME or also EUROPEAN MIDDLE TIME. This unification is in order to highlight the identity of national interests.
In order to more rationally distribute the electrical energy supplied to companies, industries and homes, and to use daylight more widely, in the summer months many countries advance clockwise by one hour. The advance is made by government provision, either only in summer or throughout the year. In the case of Cuba, France, England and Switzerland it is only during the summer but Russia, for example, has lived in summer time since 1930.
It's easy to calculate time differences between countries through the time zone map:
1- We locate the desired countries, cities or places on the map of time zones.
2- We take one of them as a reference and from it we count how many time zones there are until the other geographic object that we want to search.
3- We count the number of hours there is difference between the two points.
4- If from the selected point we count towards the east they are hours ahead and if we count towards the west, they are hours behind.
Another important element for calculating hours for different places is to consider the fractional hour system. Many countries by virtue of the conventional that is the system of time zones, do not take whole numbers of hours but fractional hours.
