Time zones correspond to standardization of schedules in different places on planet Earth.
The spindles are measured according to their longitudinal geographic position and are divided by imaginary lines called meridians.
The different times defined by the time zones are determined as a function of the solar incidence in each geographic location.
It was agreed to divide the planet into 24 time zones, this division was first proposed by the engineer Sandford Fleming, in 1878.
In 1884 the international time zone system was made official at the International Conference on the First Meridian, held in Washington, USA.
What is the time zone for?
The international standardization of time zones is what allows us to know the different times in each geographic location in the world.
Before the existence of time zones, the time at each location was determined by the position of the sun, but the lack of standardization caused confusion for travelers.
Today, it is possible to know the exact time at every point on the planet, which facilitates communication and relationships established over long distances.
How does the time zone work?
The division of time zones is done in 24 vertical bands that go from one pole to another of the planet and which are called meridians.
It was agreed to use as a reference the Greenwich Mean Time, also called the Prime Meridian, which runs through the Greenwich district of London, England.
The Greenwich Meridian is the number zero meridian and for both sides of that meridian there are another 12, totaling 24. Meridians that are to the east are rated from 1 to 12 and those to the west are rated from -1 to -12.
This system was called GMT (Greenwich Mean Time), but had its name changed to Coordinated Universal Time (UTC).
Each meridian is classified by the abbreviation UTC and the meridian number, for example, UTC + 6 or UTC - 8.
To the east of Greenwich the hours are brought forward by one hour and to the west the hours are set back by one hour.
This means that in São Paulo it is always earlier than in any other country on the African continent, Europe or Asia. On the other hand, in Chile and Ecuador, it will always be earlier than in São Paulo.
How to calculate time zones?
To understand the calculation of time zones, it is necessary to remember that the Earth completes a rotation around its own axis in 24 hours and in a counterclockwise direction (from west to east).
It is also necessary to remember that the Earth is a sphere and therefore its circumference is 360°.
To find out what the Earth's displacement is every hour, we divide the 360° by 24 hours and we get the number 15. This number represents the range of rotational movement every hour.
In other words, this means that every 1 hour, the Earth moves 15º and after the 24 hours have passed, it will have completed one revolution in relation to its axis, that is, 360º.
So we have the following relationship:
1 time zone = 1 hour = 15th longitudinal
Considering the Greenwich Meridian as central, to know which time zone in a given location, just know how many degrees there are between this location and the Greenwich Meridian to the east or West.
- East of the Greenwich Meridian: the hours are advanced (+)
- West of the Greenwich Meridian: the hours are late (-)
Examples of Time Zone Calculation
1 - Considering that it is 10 am in London, what time is it in a city A, located 60º east of Greenwich?
To find the time in city A, we divide its distance from the central meridian by 15º, which is the amplitude of a meridian. This division results in the value 4.
This means that there are 4 time zones between the two locations and therefore 4 hours apart. And as this point is located east of Greenwich, we must advance 4 hours.
Thus we find that the clocks in this city are showing 14:00.
2 - Considering that it is 6 am in London, what time is it in a B city, located 120º west of Greenwich?
The division of 120th by 15th results in 8. This means that between the two cities there is a difference of 8 hours.
As this town is located west of Greenwich, we must be 8 hours late. Thus, we find that the clocks in city B read 02:00.
Brazil time zones
Due to its large territorial extension, Brazil is located on 4 meridians and therefore has 4 different time zones:
- Fernando de Noronha time (UTC - 2): Fernando de Noronha and São Pedro and São Paulo (Pernambuco); Atol das Rocas (Rio Grande do Norte) and Trindade and Martim Vaz (Espirito Santo).
- Amazon Time (UTC - 4): Amazon (except southwest); Roraima; Rondônia; Mato Grosso and Mato Grosso do Sul.
- Brasília Time (UTC - 3): Amapá; For; Tocantins; Goiás; Federal District and all states in the Northeast, South and Southeast regions.
- Acre Time (UTC - 5): Southwest of Amazonas and Acre.
Are time zones always followed by countries?
The time zone is a geographic determination of hours, but it is not always strictly adopted by countries.
Some countries are very large and may have more than one time zone within their territory. Russia, for example, has 11 different time zones.
When there are many time zones, countries can choose to keep the same time in regions that are on different meridians to facilitate administration and communication.
One such example is China, which has four time zones, but requires the use of Beijing time throughout its territory. For this reason, in the far west of China, the sun rises around 9 am.
