We all hear the term GMT, or Greenwich Mean Time. In general, we hear it when people refer to their time zone. And many people say that they are in UTC time when what they want to say is that they are in GMT time. There is a difference between GMT and UTC – and a pretty big on to say the least. The problem is that most people don’t know exactly what a time zone is and what it is being used for. They also don’t know what the UTC standard is and what the UTC offset is used for. So let’s talk about time zones, UTC, UTC offset, and the GMT time zone specifically. You can also find a list of interesting facts about time zones at the end of this article.
Without time zones, it would be impossible for all countries on Earth to have the sun at the highest point in the sky at noon. Why? Because Earth rotates by 15 degrees every hour. This is exactly why time zones were created. Basically, the planet was split into 24 slices of 15 degrees each. Each slice is a time zone. And all time zones are coordinated using the Coordinated Universal Time (UTC) standard. This is why Eastern Standard Time is UTC-5 and Pacific Standard Time is UTC-7. The difference between a given time zone and UTC time is called the UTC offset. In other words, Eastern Standard Time has a UTC offset of minus 5 hours (UTC-5). But remember, UTC is a time standard. GMT, on the other hand, is a time zone. So it is incorrect to say that you are in the UTC time zone. Yes, UTC and GMT are being used interchangeably at the time of writing. But this does not mean it is correct.
Greenwich Mean Time, abbreviated GMT, is a time zone that covers parts of Europe, Africa and Antarctica. At the center of GMT is the Royal Observatory in Greenwich, London. Again, it is important to note that UTC and Greenwich Mean Time (GMT) are not the same. GMT is a time zone and UTC is a time standard. GMT is basically UTC+0:00. In other words, Greenwich Mean Time has no UTC offset. However, this does not mean that all countries in the GMT time zone have the same hour. Some countries are observing Daylight Saving time, so they are in the GMT+1 time zone during the warm months of the year. In fact, even the United Kingdom is observing Daylight Saving Time during the summer months. In other words, the country that invented GMT is not in GMT time all year round. During summer, the UK is in the BST (British Standard Time) time zone.
Introduced to help with naval navigation when travelling around the world, GMT was once the international civil time standard. At present time, this function is being fulfilled by the Coordinated Universal Time standard. However, in the UK GMT is still being used for civil purposes, even though not formally. The Greenwich Mean Time was created in England and adopted at the International Meridian Conference of 1884. The Earth was split into 24 time zones, with each zone being based on the Greenwich Meridian Time. Each time zone had an offset of a number of hours ahead of GMT or behind GMT. However, because Earth’s rotation is irregular and slows down every year, GMT was replaced as the world’s standard by the Coordinated Universal Time standard. UTC time is kept using extremely precise atomic clocks that are placed in various places around the world. UTC also has a leap second system in place. Because the Earth’s rotation is slowing down, there are minor differences between the UTC time and the atomic clock time. Periodically, a second is added to UTC to make up for the difference. Up to date, 27 additions have been made.
Greenwich Mean Time is being used as the standard time the entire year (there is no Daylight Saving time adjustment) in the following countries:
There are also 5 countries that are in the GMT time zone, but that observe Daylight Saving time (GMT+1):
Other territories that are in the GMT time zone include the Faroe Islands and the Canary Islands.
There are many major cities in the GMT time zone and in the GMT+1 times zone (Daylight Saving Time). Notable examples include London, Belfast, Cardiff, Dublin, Madrid, Lisbon, Edinburgh, Cork, Galway, Port, Aveiro, Reykjavik, and Danmarkshavn. The exact number of people residing in the Greenwich Mean Time Zone is not known. However, it is estimated that there are fewer people in GMT than there are in the EST time zone in the United States (around 142 million people live in the EST time zone). A little known fact is that Greenland is in the same time zone as Britain.
Now that you know everything there is to know about Greenwich Mean Time and about UTC and the UTC offset, let’s present a few very interesting things about time zones: