Two hundred years ago, nobody would have understood the question. Every town set its clocks by the sun directly overhead at local noon, so Boston, New York, and Philadelphia were all a few minutes apart from one another, and nobody cared. Then the railroad arrived, moving faster than the old system of local solar time could handle, and the mismatch became a genuine hazard.
The Problem Was Speed, Not the Sun
By the 1870s, the United States had no fewer than 300 local time standards, each set independently by a city or a railroad company. A train traveling from Maine to California crossed dozens of these zones, and a timetable that tried to account for all of them was a scheduling nightmare. Worse, it was dangerous: trains running on conflicting local times occasionally collided on shared track, since dispatchers could not be certain exactly when a train from another town would arrive.
The Railroads Force a Fix
Rather than wait for Washington to act, the major American and Canadian railroads took matters into their own hands. On November 18, 1883, at exactly noon Eastern time, the railroads implemented a system of four continental time zones for the United States, essentially the same Eastern, Central, Mountain, and Pacific divisions still used today. Cities did not have to adopt the new “railway time,” but most did within a few years simply because it was more convenient than keeping track of a dozen separate local times.
Greenwich Becomes the Starting Line
The railroad zones solved an American problem, but travel and telegraphy were becoming global, and the world needed a shared reference point. Canadian railway engineer Sandford Fleming had proposed a worldwide system of hourly time zones radiating from a single prime meridian, and in October 1884 delegates from 25 nations met in Washington, D.C., for the International Meridian Conference. They voted to designate the meridian running through the Royal Observatory in Greenwich, England, as zero degrees longitude, the baseline from which every other zone would be measured in hours ahead or behind.
Congress Makes It Official
For 35 years, standard time zones in the U.S. operated on the railroads’ own authority rather than any law. That changed with the Standard Time Act of 1918, which formally wrote the railroad zones into federal law and placed them under the oversight of the Interstate Commerce Commission, and later the Department of Transportation. It was the same act that introduced daylight saving time.
Why the System Still Makes Sense
Today the world is divided into roughly 24 principal time zones stretching out from Greenwich, though the real map is messier, since national borders, political preferences, and even a few 30- or 45-minute offsets (India and Nepal, for instance) bend the lines drawn by longitude alone. The underlying logic from 1883 has never really changed: keeping clocks reasonably close to the position of the sun overhead is useful for daily life, but keeping everyone on exactly the same clock, no matter where the sun happens to be, is useful for coordinating trains, flights, markets, and phone calls across a planet that never stops turning.