Before November 18, 1883, every city in the United States kept its own time. Each city’s noon was when the sun reached its highest point locally. Chicago’s noon was 11:50 AM in St. Louis, 11:27 AM in Omaha, 12:09 PM in Detroit. A train arriving in Pittsburgh from Philadelphia might cross through 15 different local times on a single journey.

Railroad companies maintained separate timetables for each city they served. The Pennsylvania Railroad, one of the largest in the country, ran its trains on Philadelphia time throughout its network, but cities along the route kept their own clocks. Getting on a train meant figuring out what time the railroad thought it was versus what time the town thought it was. The Pennsylvania Railroad’s timetable for 1882 showed over 100 different local times in use across its lines.

Then four men changed everything.

The Day of Two Noons

William F. Allen was the editor of the “Travelers’ Official Railway Guide” and secretary of the General Time Convention, a voluntary association of railroad executives who had been trying for years to solve the time coordination problem. He proposed a plan: divide North America into four time zones, each one hour apart, each running on a single standard time.

On November 18, 1883, at exactly noon Eastern Time, railway stations across the United States and Canada adjusted their clocks. In cities that were set ahead of the new standard, the clock was turned back. In some cities, noon came twice that day: once at the old local time and once at the new railroad time.

Chicago’s clocks were set back nine minutes and thirty-three seconds. When noon arrived at the old local time, the city waited nine minutes and thirty-three seconds, then called it noon again. Newspapers called it “the Day of Two Noons.”

This was not a government program. The federal government had no authority over timekeeping. The change was made by a private industry association, adopted voluntarily by the railroads, and then accepted city by city as mayors and merchants realized that railroad time was the only clock that mattered for commerce.

The United States Congress did not formally adopt the railroad timezone system as the law of the land until the Standard Time Act of 1918, thirty-five years later. The railroads had simply done it, and it worked, and everyone followed.

The Six Zones

The continental United States uses four main timezone zones, each an hour apart:

Eastern Time (America/New_York): UTC-5 (EST) in winter, UTC-4 (EDT) in summer. Home to the largest US population concentration. When the NYSE opens at 9:30 AM ET, most of American financial life begins.

Central Time (America/Chicago): UTC-6 (CST) in winter, UTC-5 (CDT) in summer. The middle of the continent. Chicago, where railroad time was first debated, anchors this zone.

Mountain Time (America/Denver): UTC-7 (MST) in winter, UTC-6 (MDT) in summer. The Rockies zone. Some areas of the Mountain zone, particularly in Indiana and parts of Arizona, have complicated histories of non-standard or non-DST observation.

Pacific Time (America/Los_Angeles): UTC-8 (PST) in winter, UTC-7 (PDT) in summer. California, the West Coast.

Alaska Time (America/Anchorage): UTC-9 (AKST) in winter, UTC-8 (AKDT) in summer. Alaska is enormous: at some 586,000 square miles, it is larger than Texas, California, and Montana combined. At its western extreme, the Aleutian Islands continue almost to the International Date Line.

Hawaii-Aleutian Time (Pacific/Honolulu): UTC-10 (HST) year-round. Hawaii does not observe DST. The Aleutian Islands, technically in the same IANA zone for part of the chain, do observe DST under America/Adak.

The Arizona Exception

Arizona largely does not observe daylight saving time. The state stays on Mountain Standard Time year-round: UTC-7, always. The reasoning is direct: Arizona is hot. Summer afternoons in Phoenix regularly exceed 43 degrees Celsius. Adding an hour of evening daylight when temperatures peak is unwelcome. Arizona wants more morning hours and fewer blazing evenings.

The Navajo Nation, which spans northeastern Arizona into New Mexico and Utah, does observe DST, following federal policy that applies to federally recognized tribal nations. The Hopi Reservation, which sits entirely within the Navajo Nation but is a separate sovereign nation, does not observe DST (following Arizona state practice). This creates a geographic curiosity: driving through northeastern Arizona, you can cross into DST (Navajo Nation), then back out of it (Hopi Reservation), then back into it (Navajo Nation again), then out again (Arizona proper). This is the most timezone-dense state line crossing in the world.

Indiana: A Complicated History

Indiana spent decades in a state of timezone confusion that would require a dissertation to fully document. For most of the 20th century, Indiana counties observed a patchwork of different timezone practices: some observing EST year-round, some CST year-round, some observing DST and some not. Parts of Indiana were effectively in different timezone relationships with neighboring states depending on the season, the county, and the decade.

The state standardized in 2006, when Governor Mitch Daniels pushed through legislation requiring uniform statewide observance of Eastern Time with full DST participation. The debate was fierce: some communities had scheduled their entire economic and social lives around being in a different effective timezone than the rest of the state. “Indiana time” had become a genuine cultural and commercial identity.

DST: A Century of Controversy

The United States adopted daylight saving time nationally for the first time in 1918, with the Standard Time Act, as a wartime energy-saving measure. It was repealed in 1919. Reintroduced in 1942 as “War Time.” Peacetime DST was left to state and local discretion from 1945 to 1966.

The result was that in the 1950s and early 1960s, some cities observed DST and some didn’t, often changing their policies year to year. The same 35-mile stretch of Interstate highway might cross two or three different effective times depending on which towns along it had decided to spring forward that year.

The Uniform Time Act of 1966 standardized DST across the United States, though it preserved the right of states to opt out entirely. The Energy Policy Act of 2005 extended DST by four weeks starting in 2007: it now runs from the second Sunday in March to the first Sunday in November.

The Sunshine Protection Act, which would make DST permanent year-round, passed the US Senate unanimously in March 2022. It stalled in the House and did not become law. The debate about permanent standard time versus permanent summer time continues, with scientists, pediatricians, and sleep researchers generally advocating for permanent standard time, and retail and recreation industries generally advocating for permanent summer time.

The Broadcasting Clock

American network television scheduling has been organized around the Eastern/Pacific timezone division for decades. Prime time runs 8-11 PM Eastern, 7-10 PM Central, and a complicated arrangement on the West Coast: the same broadcast often runs at 8 PM Pacific (tape-delayed from the live East Coast feed) or at the exact same clock hour, meaning Pacific viewers watch events they know have already concluded three hours ago.

Super Bowl Sunday in the Pacific timezone means a late finish. State of the Union addresses at 9 PM Eastern are 6 PM Pacific, still in the dinner hour. The Eastern timezone sets the national programming clock for a country spanning 60 degrees of longitude.

Cinematic time

Robert Zemeckis’s Back to the Future (1985) features a single time machine and a single local timezone: Hill Valley, California, Pacific Time. The film’s central scene involves two clocks: the clock tower stopped at the exact moment it was struck by lightning in 1955, and Doc Brown’s modified DeLorean. The tension is entirely temporal.

High Noon (1952), the Western that uses real time, runs at Pacific Mountain Time (no one specified), in a town where the clock on the wall approaches 12:00 as the plot approaches its climax. The clock is the film’s antagonist. Time is the gunfighter.

The United States produces more timezone-anxiety content than any other culture: the countdown, the deadline, the race against the clock. A country that industrialized around the railroad timezone, that split itself into four for commercial convenience, that argues about DST in every Congressional session, has made the clock both tool and symbol.

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