Visit the home of Greenwich Mean Time, stand on the world-famous Prime Meridian Line and come to London's only Planetarium. Royal Observatory Greenwich is Britain’s oldest purpose-built scientific institution. Founded in 1675, it is the birthplace of modern astronomy, and the home of Greenwich Mean Time and the Prime Meridian. Today the site holds a unique position as a museum, science attraction and historic site: the national centre for the public understanding of astronomy past and present. Stand on the historic Prime Meridian Line Place one foot in the west and one in the east at the Prime Meridian of the World. Since the late 19th century, the Prime Meridian at Greenwich has divided the eastern and western hemispheres of the Earth - just as the equator divides the northern and southern hemispheres. The Prime Meridian also helped to establish the world time zone system we still use today. Learn all about Greenwich Mean Time (GMT) at the Royal Observatory, and discover how Greenwich came to be the home of time.