Throughout most of
written history, time keeping was essentially a
local affair. Every town set its clocks according
to the motions of the Sun, and Noon was defined
as the time when the Sun reached its maximum
altitude above the horizon. Each town had its own
official timekeeper to calibrate a town clock to
the Sun's motions. This town clock represented
the "official time" in that town, and
the citizens would set their own watches and
This system of local
timekeeping was sufficient so long as the
majority of people stayed in one place most of
their lives. But, as technology allowed people to
move across the country, a new system became
necessary. In the United States and Canada
especially, the railroads found it near
impossible to construct accurate timetables for
stops, since each stop was on a different time.
Timetables could only become more efficient if
every city and town along the rail network
adopted some standard method of keeping time.
In 1878, Canadian Sir Sanford
Fleming proposed that the globe be divided into
24 time zones, each 15 degrees of longitude in
width. Since the Earth rotates once every 24
hours on its axis and there are 360 degrees of
longitude, each hour of Earth rotation represents
15 degrees of longitude. American railroad
companies began using Fleming's time zones in
1883. In 1884, members of the International Prime
Meridian Conference agreed that the longitude of
Greenwich, England, would become zero degrees
longitude and established the 24 time zones
relative to the "Prime Meridian."
Today, most nations use the
time zones suggested by Fleming. The map below
shows all 24 of the time zones currently in use.
National boundaries and political matters
influence the shape of the time zone boundaries.
China, for example, uses a single time zone
instead of the five it "should" have.
The second map shows the six different time zones
in use within the borders of the United States.
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