Greenwich Mean Time (GMT) is one of the many time zones that exist nowadays. It refers to the name used for mean solar time. It lies in longitude (0°) of the Royal Greenwich Observatory in England. The meridian at this longitude is known as the prime meridian or Greenwich meridian. Of all the time zones, why does Greenwich Mean Time matter? Why do people need it if it is in longitude (0°)? Find the answers in this article.

Greenwich Mean Time

According to Britannica, astronomers have used Greenwich Mean Astronomical Time (GMAT). It is when the astronomical day began at noon at longitude (0°), which is in accord with scientific tradition. GMT was adopted in 1925 by the astronomers because they used the astronomical day to begin at midnight. This is also the same time as civil day. As a result, some people were confused with the terminology used.

To solve the dilemma, the International Astronomical Union changed the Greenwich meridian's designation to Universal Time in 1928. Nowadays, people use Universal Time in a modified form as Coordinated Universal Time (UTC). Like the GMT before, UTC serves to accommodate the timekeeping differences between atomic time and solar time. However, some individuals still use the term Greenwich Mean Time since it represents civil time in Britain.

How GMT Time Become the International Standard

Though UTC is currently used right now as the reference for other time zones, it is still essential to understand how GMT became the international standard before. Greenwich Meridian was recommended as the Prime Meridian of the World in 1884. This is because the United States had already chosen Greenwich as the basis for its national time zone system. Aside from that, 72% of the world's commerce depended on sea-charts which used Greenwich as the Prime Meridian. The recommendation of making Greenwich Mean Time as the international standard was based on the argument that naming Greenwich as Longitude 0º would be of advantage to the most significant number of people.

Greenwich Mean Time refers to the yearly average (mean) of the time each day when the sun crosses the Prime Meridian. GMT, which lies at the Royal Observatory Greenwich, is one of the most significant time zones since it was used before as a reference for other time zones. Although it has been replaced by the Coordinated Universal Time, GMT still matters. This is because Greenwich Mean Time is still used as a legal time in Britain in the winter.