The Prime Meridian

The Prime Meridian is an imaginary line of longitude that is designated as 0 degrees longitude. 

It passes through the Royal Observatory in Greenwich, London, England, and serves as the reference point for measuring longitude in the Eastern and Western Hemispheres. 

The Prime Meridian divides the Earth into 

• the Eastern Hemisphere and 
• the Western Hemisphere, and 

is used as a standard reference point for navigation and timekeeping. 

It was first established at an international conference held in Washington D.C. in 1884, and has since been recognized as the standard reference line for longitude by the International Meridian Conference. 

The concept of the Prime Meridian and longitude was first proposed by 

• the Greek mathematician Hipparchus in the 2nd century BCE.

Prior to the establishment of the Prime Meridian, various countries and organizations used their own reference points for measuring longitude.

The Prime Meridian is used as a standard reference point for 

• navigation, 
• cartography, and 
• timekeeping.

Greenwich Mean Time (GMT) is based on the time at 

• the Royal Observatory in Greenwich, which is 
• located on the Prime Meridian.

The Prime Meridian has become a popular tourist destination, with visitors often taking photographs of themselves standing on either side of the line.

There are several other important meridians, such as the International Date Line and the 180th meridian, which are used to define time zones and the date line.