We explain what the Greenwich meridian is and what the history of this imaginary line is. Also, how it is used for location, navigation and planet time.
What is the Greenwich Meridian?
The Greenwich meridian, also called zero meridian, base meridian or prime meridian, is the imaginary vertical line that divides the world map into two identical halves and from which the length is measured. It is also the meridian that marks the world standard base time to which hours are added or subtracted to determine the time slots of each country.
The location of this imaginary line gets its name because passes through the British town of Greenwich, in England and because the Royal Greenwich Observatory was located there, built in 1675. In addition to the United Kingdom, the meridian crosses other countries, and it is common to find signs in France, Spain, Algeria, Mali, Burkina Faso, Ghana or Togo that mark its location. location.
The Greenwich meridian divides the planet into two semicircles of 180° each, segmented into 15° time zones (result of dividing 360° of the complete circumference by 24 hours).
Characteristics of the Greenwich Meridian
The Greenwich meridian has the following characteristics:
- It is the 0° meridian, from which the planet is divided into two hemispheres: the east and the west.
- It is considered the meridian of origin worldwide.
- It crosses the English town of Greenwich, hence its name.
- It was adopted as the basis of the planetary coordinate system in 1884.
- It is the basis for calculating time around the world.
History of the Greenwich Meridian
The decision to adopt the Greenwich Meridian as the basis for the time and coordinate system was made in 1884 in Washington, DC. United States, at a convention attended by 41 delegates from 25 countries.
There the universalization of this system was agreed, since in various places, such as Paris, Rome, Copenhagen, Jerusalem and Saint Petersburg, different meridians were used as a guide. The resolution had the disapproval of countries such as the Dominican Republic and the abstentions of France and Brazil, but Greenwich was finally imposed as the 0° meridian, which persists to this day.
GPS systems: There is a very slight angular difference (5.3 seconds) between the Greenwich meridian and the reference meridian used by contemporary GPS systems. This is because a more precise definition of the reference meridian was introduced in 1984, known as the IERS (International Earth Rotation and Reference Systems Service) Reference Meridian, which states that the Greenwich meridian is about 102 meters away. east of its original position.
The Greenwich Meridian and time zones
The Greenwich Meridian is the reference point from which all time zones on the planet are calculated.. Coordinated Universal Time (UTC) has its 0 point on this meridian and is the global time standard in use today.
Starting from UTC 0, the time zones of the rest of the countries are calculated. For example, if a place has a UTC+3 time zone, it means that there is three hours later than the places crossed by the Greenwich Meridian. If a place has UTC-5, it means it is five hours earlier.
Latitude and longitude
Latitude is an angular measurement used to determine the position of a point on the Earth's surface in a north-south direction. It is measured in degrees and goes from 0° at the equator to 90° at the poles.
Instead, longitude is an angular measurement used to determine the position of a point on the Earth's surface in an east-west direction. Like latitude, it is measured in degrees, and goes from the Greenwich meridian (0°) towards the east and west, to a maximum of 180°, where the Greenwich antimeridian is located.
With latitude and longitude, the geographical coordinates of any point on the planet's surface can be known.. For example, Mexico City is located at 19° north latitude and 99° west longitude. This means that it is located 19° north of the equator and 99° west of the Greenwich meridian.
References
- Hernandez, L. (2022). Greenwich: why did it become the unique meridian of reference and origin of geographical longitude? LaSexta. https://www.lasexta.com/
- McKeever, A. (sf). Curiosities (and craziness) about the world's time zones. National Geographic. https://www.nationalgeographic.es/
- Galileo Galilei Planetarium. (sf). The Earth. Rotational movement. Time zones. https://planetario.buenosaires.gob.ar/
- Velasco, M. (2024). Greenwich Meridian: the clockmaker who figured out how to measure longitude at sea. The Vanguard. https://www.lavanguardia.com/
