The Royal Observatory at Greenwich is home to both time and space: Greenwich Mean Time (GMT) and the Prime Meridian. But have you ever stopped to ask what the Prime Meridian is, and why it's in Greenwich? Why are all time zones across the world based on GMT? What is the longitude? Why is the meridian moving? A succinct history of the Meridian Line and its importance in defining international time standards, On the Line: The Story of the Greenwich Meridian breaks down complex topics in manageable articles, accompanied by eighty color illustrations and fun trivia to aid understanding. This insightful, concise guide reveals why international time standards are based around the Greenwich meridian--Longitude 0 --where east meets west, and details the important discoveries made at Greenwich that led to time as we know it.