Most people don’t know what UTC is and what times zones are. To shed light on the matter, let’s talk about what time zones really are, what UTC is, and then list the major countries and cities in UTC. Also, let’s see the differences between UTC and Greenwich Mean Time and then list some fun time zone facts. And did you know that UTC is not a time zone? Let’s see why!

What Is a Time Zone?

A time zone is a region on Earth that observes the same time. This way, it will be the same hour in all the countries and the cities in the time zone. As you can imagine, noon is at different times in each country, which means that noon (12 AM) would be observed at different times from country to country. Without a standard time that all countries in a time zone must observe, the countries would never observe the same time. This has many implications. Time zones are very important for commercial and social activities. As long as two countries are in the same time zone, you won’t have any communication issues. If the person you are speaking to or who ships your product is in a different time zone, it may be midnight your time when it’s noon his or her time. You can imagine the trouble you would have communicating with people who are 6 to 12 hours ahead or behind your time. Also, time zones are very important for military purposes. The military uses different names for the different time zones, but the way they work is exactly the same. For example, UTC is Zulu Time in military jargon.

What Is UTC?

UTC stands for Coordinated Universal Time. This is the primary time standard in the world, and the standard after which the entire world regulates its time. Your clock is regulated by the Coordinated Universal Time standard. UTC is not a time zone, even though people use it as one. Again, UTC is a time standard. UTC has a difference of less than one second of mean solar time at a longitude of 0 degrees. Even though this time standard started being used from the start of 1960, it was officially adopted later, in 1967. Of course, the time standard has undergone several adjustments over time. The UTC we use today was implemented in 1972. It contains what is called “leap seconds,” which makes it easy to adjust the time in the future if need be. Why adjust the UTC? Because of irregularities in the Earth’s rotation rate. Because of this irregular rotation rate, UTC is slowly drifting away from the extremely precise atomic time. As such, it needs to be adjusted periodically. And another thing to keep in mind is that UTC will never change for DST (Daylight Saving Time).

UTC and Greenwich Mean Time: The Differences

Many people say that they live in UTC time zone. This is, in fact, an incorrect statement. Why? Because UTC is a time standard, not a time zone. What they should be saying is that they live in the GMT time zone. GMT, an abbreviation for Greenwich Time Zone, is the time zone that observes UTC+00:00 time (exact UTC time). The plus sign is known as the offset from Coordinated Universal Time. It tells people by how many hours their time is offset from UTC. For example, the United States is in several times zones. Colorado is in UTC-07:00, while California, Nevada and Oregon are in UTC-08:00. Samoa has a time offset of UTC+13:00. Baker Island and Howland Island, on the other hand, have a negative offset of UTC-12:00. The differences in time between various countries on Earth can be huge. And keep in mind that GMT will never change for DST (Daylight Saving Time). However, some countries who observe DST will switch to a different time zone for this purpose. For example, the United Kingdom (who established GMT) switches to BST (or British Summer Time) during the summer months. As you might have guessed it, BST time is 1 hour ahead of GMT time.

Major Countries in the GMT Time Zone (Using Coordinated Universal Time)

Many countries in Europe and Africa have an offset of UTC+00:00. This means that they are in the GMT time zone. Here are the countries that use standard time all year round:

• Burkina Faso in Africa
• The Gambia in Africa
• Mauritania in Africa
• Ghana in Africa
• Côte d’Ivoire in Africa
• Guinea in Africa
• Liberia in Africa
• Mali in Africa
• Senegal in Africa
• Guinea-Bissau in Africa
• Sierra Leone in Africa
• Togo in Africa

There are also some Atlantic Islands:

• Greenland
• Iceland
• Saint Helena
• Ascension Island
• Tristan da Cunha

In Europe, the following territories are in GMT time zone, but only in the Northern Hemisphere winter period:

• Alderney
• United Kingdom
• Guernsey
• Sark
• Faroe Islands
• Herm
• Isle of Man
• Jersey
• Ireland
• Portugal (remember that the Azores area has an offset of UTC−01:00)

Although there are no official figures, the number of people who live in the GMT time zone is in the hundreds of millions. 

Important Cities in UTC

As you can imagine, there are a lot of major cities in GMT time zone (observing UTC time). However, keep in mind that many of these cities are not observing UTC time all year round because of Daylight Saving Time and other time zone adjustments. Here are the major cities that observe UTC at one time or another during the year:

• London
• Casablanca
• Dublin
• Porto
• Bissau
• Lisbon
• Ponta Delgada
• Ittoqqortoormiit
• Accra
• Reykjavik

Interesting Time Zone Facts

Even though UTC is a time standard and GMT is a time zone, UTC is being used even by official sources. It is expected that UTC will replace GMT in the near future. So it is not a big mistake to say that you are in a UTC time zone. Now that you know what Coordinated Universal Time is and where it applies, let’s take a look at some interesting time zone facts:

• Most time zones are offset from UTC using whole hours. However, there are countries that have offsets that contain parts of an hour. For example, India is in UTC+05:30. Also, the Nepal Standard Time is basically UTC+05:45.
• There are proposals to replace the UTC with another standard – one that does not use leap seconds to adjust the time after the atomic clock time. 
• The first leap second was added on June 30, 1972. In total, there have been 27 seconds added to UTC over the years, up to date.
• The length of the mean solar day is increasing because the Earth’s rotational speed is slowly decreasing because of the tidal deceleration effect.
• The Earth will keep slowing down its rotation, so more and more leap seconds will be added in the future to compensate.
• Daylight saving time was created to help people enjoy more active hours during daylight.
• The differences in time zone have an interesting effect. While it may be Monday where you live, it may be Tuesday or even Sunday where the person you are talking to lives.
• It’s easy to forget about time zones when travelling by plane over long distances. Be careful not to call somebody at 3 in the morning thinking it’s 10 AM there as well.
• Both cell phones and computers adjust time automatically when you travel from one time zone to another. But you will have to manually adjust your watch.
• Did you know that you can have two birthdays? Just take a plane to another time zone and you can turn your clock back by anywhere from 3 to 12 hours.