What is the Greenwich meridian and how was it discovered?

Answer 1

The Greenwich Meridian (or prime meridian) was not discovered, it was invented/established.

It was created to standardise navigation and also to establish relative time zones. It is called the Greenwich meridian only because it passes through the borough of London named Greenwich where the observatory that proposed it was located. The Prime Meridian ("Greenwich meridian") is an imaginary line between the north

and south poles that passes through the transit room of the Royal Observatory in

Greenwich UK.

All time zones are based upon the time at the Greenwich meridian, hence time worldwide is relative to GMT...Greenwich Mean Time. Time zones are related using terminology such as GMT + 2 or GMT - 9, indicating the number of hours to add or subtract from GMT.

The Greenwich Meridian is also the "0" meridian in the geographic system of locating a place on the globe using latitude and longitude. Latitude plots distances north and south of the equator while Longitude plots locations based upon distances East or West of the Prime meridian. Latitude goes from Zero, to 90 degrees either North (North Pole) or South (South Pole). Longitude runs East and West from the Prime (Greenwich) meridian and meets again at the opposite side of the globe, namely 180 degrees around.

For time, the only other factor is the presence of the International Date Line which is roughly opposite the Prime Meridian. The Date Line runs through the middle of the Pacific Ocean, jogging a little east and west to avoid splitting the date in island chains. When crossing the date line, the traveler gains or loses one day.

You might also be interested to reflect on the fact that, since the Greenwich meridian was established and marked on the ground in the floor of the Greenwich observatory in 1884, continental drift (the widening of the Atlantic Ocean) means that the meridian on the reference geoid no longer matches up with the mark on the ground.