What is Greenwich Meantime (GMT) and how does it Relate to World Time?
GMT or Greenwich Mean Time is usually used for Coordinated Universal Time (UTC). It does not take into account the precise accuracy on the basis of fractions of a second. Usually, most people refer to GMT as a term which can be interchanged with UTC. However, there are some differences between these two concepts. In this article, we will tell you everything about Greenwich Mean Time and its relation to other world time zones.GMT – An Overview
In 1884, Greenwich Mean Time was adopted as the world’s standard time. This happened during the Washington Meridian Conference. During this conference, Universal Time was also established. Universal Time gave rise to the international 24-hour time zone system. As a result, every time zone refers back to GMT on the prime meridian. Since the 19th century, prime meridian at Greenwich, England has served as the line of reference for GMT. The time of time of this city is taken as a reference for the whole world. The time of other cities of the world only calculated related to the time of this city.
At first, Greenwich Mean Time was calculated as per the 24-hour clock, beginning at noon. However, the scenario changed in 1925, when the day of GMT was considered to start at midnight. After a while, GMT Greenwich Time zone was renamed to Universal Time (UT). Sometimes, it is also referred as UT0. On the other hand, t is called UT1 when irregular movements of terrestrial poles are taken into account. Also known as Chandler Wobble, this happens because Earth’s poles never spin in a straight line.
Development of Different Time Systems
UT1 was followed by the formulation of a new concept. This one was known as UT2. It aimed to correct certain seasonal variations to give precise and accurate time. With the development of mechanical clocks, Atomic Time came into existence.
There are many different time services around the world. Their combined mean version is used as International Atomic Time (TAI). This one is the international atomic time scale. It is based on many different atomic clocks. However, unlike UT1, developed from GMT, it does not take into account the Earth’s rotation. As a result, one more standard for civil time is Coordinated Universal Time (UTC).
Development of UTC
The difference between UTC and TAI are important seconds. If you add or subtract seconds from TAI, it results in UTC. This difference is also known as a leap second. A leap second is measured by an atomic clock, and added to or subtracted from UTC, to make it similar to astronomical time within 0.9 second. All the timing centres in the world like to keep their timescales synchronised with UTC. Therefore, all these scales are known as Coordinated Universal Time.
Usually, GMT is often called UTC. However, this reference means UT1. Since 1972, UTC has been the universal time broadcast by radio stations around the globe. Popularly, it is known as GMT Greenwich Mean Time zone. UTC is unofficially known as Zulu Time. It is also used in aviation to avoid any confusion between time zones and daylight saving time.
Some Other Time Systems
Astronomers also used other time systems to measure time. Some popular examples include:
Terrestrial Dynamical Time
Terrestrial Dynamical Time (TDT) is 32.184 seconds ahead of TAI. Terrestrial Dynamical Time is also called Terrestrial Time (TT). It has a unit of duration 86400 SI seconds. Astronomers use TDT to calculate planetary positions with respect to the Earth’s center. The difference between UT1 and TDT is known as Delta T. TDT was first used in 1984. Prior to TDT, astronomers used Ephemeris Time (ET) to gather information about planetary positions. Ephemeris Time was the closest approximation before atomic clocks. It helped astronomers keep a track of planetary positions and motions.
Other important time systems in the world include :
Barycentric Dynamical Time (TDB)
Barycentric Coordinate Time (TCB)
Geocentric Coordinate Time (TCG)
GMT Greenwich Time zone is recognized by people all across the globe. Over time, people have come to adopt this system as a standard for civil time. However, other time zones mentioned in the article are also equally important for different purposes. Understanding how different time zones work will give you a better idea about their purpose and functioning. The standard Greenwich clock is located at the Royal Observatory in Greenwich, England.