Difference Between Similar Terms and Objects

Difference Between GMT and BST


Because the Earth is elliptical and goes around the sun on its orbit, a huge time difference exists among the different countries located in its different parts. Its inhabitants created time zones which are based on the time when the mean sun passes through the Greenwich Observatory in London. This is referred to as Greenwich Mean Time (GMT) which is a time zone which is similar to the Coordinated Universal Time (UTC). It refers to mean the solar time which is observed in the Royal Observatory in Greenwich, London and is also known as Zulu time.

Its use started in the United Kingdom during the 1800s when the nation made some developments in its maritime capacity. It is used to calculate their longitude based on the Greenwich meridian. Mariners from other countries later adapted this practice which led to the use of GMT as a worldwide reference for time zones in different parts of the world. It uses two different conventions for numbering hours.

One convention refers to noon as zero hours based on the work of Ptolemy. It does not necessarily mean that it is the exact time when the sun crosses the Greenwich meridian because of the Earth’s uneven tilt and orbit. This led to the creation of a fictitious mean sun which is the annual average of the uneven motion of the sun, thus the name Greenwich Mean Time. The other is the civil convention which refers to midnight as zero hours which is based on the practice of the Romans.

Today, GMT is used in the United Kingdom only during the winter. In the summer it uses the British Summer Time (BST). It is the time zone or civil time used in the United Kingdom which is ahead of the Greenwich Mean Time by one hour (GMT/UTC + 1).
It was introduced and became very popular in the early 1900s. Its use starts at the onset of the summer months which begins on the last Sunday of March and ends on the last Sunday of October.

It was meant as a daylight savings time adding an hour to GMT to make use of the extended daylight of summer. For two years it was adapted by the United Kingdom as their standard time but was later reverted to summer time because of an increase in accidents during the day.


1.GMT is Greenwich Mean Time while BST is British Summer Time.
2.GMT is similar to Coordinated Universal Time (UTC) which is the standard time zone of the world while BST is GMT plus one hour.
3.The use of both GMT and BST started in the United Kingdom with GMT being used during the winter and BST during the summer.
4.GMT utilizes a fictitious mean sun while BST does not.
5.GMT has been used by British mariners since the early 1800s while BST was introduced in the early 1900s.
6.The use of BST in the United Kingdom starts on the last Sunday of March and ends on the last Sunday of October while the use of GMT starts on the day following the end of BST.

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