> Which capital city is closest to the prime meridian?And the answer: London. Photo courtesy: WikipediaLike the equator, the prime meridian is an imaginaryline that divides the Earth, but instead of running east and west, it runs northand south. The prime meridian divides the Eastern Hemisphere from the WesternHemisphere, and runs through Greenwich England, which is a borough of London.It's considered to be 0 degrees longitude.While meridians are lines that humans create as points of reference, they servean integral purpose in astronomy. Essentially, when a meridian is established,it serves as the "zero" reference line for astronomers – of course, any goodgraph has a reliable zero value. By use of meridians, astronomers can create areliable map of the sky and its stars. Since the late 19th century, the prime meridian has been officially located inGreenwich, England. Before Greenwich was established as the point of reference,local towns and cities kept their own time; there was no set rule or standard.As national and international rail lines began to take form, the need tostandardize time became grew. Since the United States and 72% of the world'scommerce had already based their time zone off of that of Greenwich, it wasadopted as the official prime meridian of the world. Photo courtesy: Royal Museum of Greenwich.Fun fact!Before standardized time, coordinating travel was, well, tricky. Oftentimes,governments would publish maps running the prime meridian through their capitalcity. For example, a French map would locate Paris at 0 degrees longitude, whilea Chinese map would use Beijing. Sometimes, local maps would center their townor city along the prime meridian!