UTC - GMT - AM/PM - World Time Zones

In geography, the time zone is each one of the twenty-four areas in which the Earth is divided, following the same definition of chronometric time. They are so-called because they have a spindle shape, and are centered on meridians of a longitude that is multiple of 15°. Previously, the apparent solar time was used, so the time difference between one city and another was a few minutes if the cities compared were not on the same meridian. The use of time zones partially corrected the problem, by synchronizing the clocks of a region to the same mean solar time.   All-time zones are defined with the so-called Coordinated Universal Time (UTC), a time zone centered on the Greenwich meridian (also known as the zero meridians), which is named after passing through the Royal Observatory of Greenwich, in the Great London.   Since the Earth rotates from west to east, when going from one time zone to another in an easterly direction, one hour must be added. On the contrary, when going from east to west you have to subtract one hour. But all places on the same meridian must have a similar time, and therefore the bands are set from north to south (vertically) to establish a standard time system for everyone. The 180° meridian, known as the international date change line, marks the change of day.

UTC Time Zones - UTC General Info

In 1928, the International Astronomical Union introduced the term UTC (Coordinated Universal Time) which basically corresponds to the Greenwich mean solar time calculated at midnight because it is the time of the lower passage of the sun over the earth. This UTC time must be corrected for the movements of the Earth's poles, obtaining a corrected UTC time.
  This corrected UTC time was widely used until 1955 when the atomic clock was invented, a clock that is based on the levels of separation of the energy of the Cesium 133 atom, which is extremely precise and is not affected by external conditions, completely replacing in this way astronomical observations for time measurements.   As it is not possible, for different reasons, to have a single standard clock, it is resorted to comparing world atomic times; From the average of all of them, the International Atomic Time (TAI) is obtained, which is much more precise than the universal one. However, the UTC system is used by the scientific community and is the basis of the current one. From that time zone, the hours will be modified, Greenwich being O time.

GMT and UTC

GMT (Greenwich Mean Time) is often confused with UTC (Universal Time Coordinated) but, although they have the same time, the difference is that GMT is a time zone and UTC is a time standard.   The time can be displayed using either the 24-hour format (0-24) or the 12-hour format (1 - 12 am / pm), but it differs in what time is said. If we take the example of 1 p.m. it is correct to say 1 p.m. GMT, but in UTC the correct thing is to say 13 hours UTC.   We already mentioned that GMT and UTC share the same current time in practice, but we will comment on this basic difference between these two terms: GMT is a time zone officially used in some European and African countries. While UTC is not a time zone, but a time standard that is the basis for civil time and time zones throughout the world.

World Time Zones General Info

Time is an abstract concept created by man to order events in sequences and to orient oneself concerning a certain moment. Since the beginning of humanity, man has used his knowledge of heaven to measure time. The annual solstices and equinoxes provided them with reliable points to build a map of the year, and the constellations provided useful markers for time. The Romans and Greeks considered the time to be one-twelfth of the time from sunrise to sunset.   For hundreds of years later, the sun was also used as a marker of the hours of the day employing basic instruments such as the sextant, (an instrument that was also used in navigation) but these instruments and the first clocks that appeared were of doubtful precision. Likewise, astronomers and geographers used different meridians according to their time or country.   At the end of the 19th century, due to the appearance in the United States of land means of locomotion, trains, the need arose to coordinate the departure and arrival times at the different points of the route. In short, establish a uniform standard of time. It was in 1879, when Sir Sandford Fleming, a Canadian railway engineer, proposed a solution to establish a standard time system.   A division in the circumference of the earth was determined using the meridians that would divide the surface into 24 time zones of 15 degrees of separation each.   Due to this defined separation, in 1884, the need to know the meridian origin of this division was raised, and for this reason, an international conference known under the name of "international meridian conference is held in the city of Washington during October”, Where three candidatures are presented for this clarification. Washington, Greenwich, and Paris.   After several presentations, the Greenwich candidacy is chosen and it is marked that the Zero meridian would be the one that passes through that observatory. From then on, all hours should be measured from that location.

AM/PM General Info

AM and PM are two acronyms of Latin origin, “Ante Meridiem”, which means “Before noon”, and “Post Meridiem” which translated into Spanish is “after noon”. Both acronyms are used to refer to each of the 12-hour periods into which the day is divided.  
Taking into account the 12-hour system, the AM indicator is a period starting at midnight (00:00) until 11:59. Meanwhile, the PM indicator starts at noon (12:00) until 11:59 at night. The 12-hour system is used in many countries, such as Mexico, Venezuela, Colombia, Uruguay, Honduras, Canada, among others.   For its part, the 24-hour system, also known as military time, avoids the use of the acronyms AM and PM due to the continuous counting after noon, for example, 1 o'clock is equivalent to 1 p.m., and so on. successively. Currently, it is a widely used system and preferred in writing to avoid confusion regarding the time when the events occurred.   However, there are countries where they use both systems, using the 12-hour system in the informal dialect, such as it's 5 in the afternoon, it's 3 in the morning.   The AM and PM indicators are observed in digital clocks to differentiate and allow the individual to know of the time, whether it is before or after noon, although there are digital clocks with a 24-hour system. In this sense, the individual must choose which system is best suited.