Why were times zones established and how many are there?

Answer 1

The system of worldwide time zones was first proposed In 1878 by the Canadian Sir Sanford Fleming. It was made for the convenience of trade & commerce, especially for the railway industry. There are 24 times zones which was based on the number of hours it takes the Earth to rotate on its axis.

Answer 2

The inventions of the train and the telegraph made it easier for people of different areas to interact. However, before the 19th century, only cities, towns, villages, etc. that were on the exact same line of longitude had the same time, known as local mean time (LMT). If you measure along which longitude is the sun directly overhead at intervals of exactly 24 hours, the average length of a solar Earth Day, for a whole year, then calculate the average of all of the longitude measurements, those daily measurement times would be exactly 12 o'clock noon along that average longitude. That means that if City A were along 1° east longitude and City B were along 2° east longitude, the time in City A would be four minutes behind the time in City B. Having as many "time zones" as we had cities became especially troubling when railroad workers had to coordinate when each train would be using a certain length of track. Each train's schedule was written in the time of the city where the train originated, and trains from many cities used the same length of track. That is why it was the railroad industry more than any other group that pushed for the creation of standard time zones.

Each time zone is identified by how many hours it is behind or ahead of Coordinated Universal Time (UTC). For example, the standard time along the east coast of the United States, called Eastern Standard Time, is UTC-5 because it is five hours behind UTC. Every year they advance their clocks by one hour from March to November (Eastern Daylight Saving Time). Since they add one hour to UTC-5, they are in the UTC-4 time zone during Daylight Saving Time (DST).

UTC is so close to Greenwich Mean Time (GMT), the local mean time at the Royal Observatory at Greenwich, England, that many people think the two phrases are interchangeable.

Not counting Daylight Saving Time, which is more commonly known as Summer Time among the countries that use it, there are today a total of 40 time zones worldwide. The 40 offsets from UTC of the world's standard time zones are -12, -11, -10, -9.5, -9, -8, -7, -6, -5, -4.5, -4, -3.5, -3, -2, -1, 0, +1, +2, +3, +3.5, +4, +4.5, +5, +5.5, +5.75, +6, +6.5, +7, +8, +8.75, +9, +9.5, +10, +10.5, +11, +11.5, +12, +12.75, +13 & +14. There are two additional UTC offsets that are used only as DST offsets, UTC-2.5 and UTC+13.75. Some lists do not include UTC-12 because it applies only to Baker Island, which is not officially inhabited.

A single time zone can have many names. For example, depending on the location, UTC-5 is called Eastern Standard Time, Central Daylight Saving Time, Cuba Standard Time, Colombia Time, Ecuador Time, Peru Time, Acre Time, and Easter Island Summer Time.