It was 1884 that "Universal Time" was established using the longitude line running through Greenwich in London, England. It's the origin of why we say GMT, or "Greenwich Mean Time," to use as a standard point of reference for time zones. Before the notion of standard time, cities around the world were using the local position of the sun to set their own official clocks. But this became a problem in the second half of the 19th century, when new technology gave rise to new forms of transportation, like steam engines and trains. Trains could travel so fast over such long distances that train conductors kept needing to readjust their clocks to local, uncoordinated time. They would have to do it many times on a single long train ride, and it was all very confusing. And so in 1879, a man named Sanford Fleming suggested that we divide the world into 24 hour time zones. Each time zone would be 15 degrees of longitude (those vertical lines on the globe). And then, a few years later, in 1884 at the International Meridian Conference in Washington, D.C., delegates from around the world voted to make the local time at Greenwich the universal standard time on which all other time zones would be based. Greenwich was chosen because there was a famous Royal Greenwich Observatory, which many maps already used as a reference point.