|
he period called the day is the time for the Earth
to rotate once upon its axis with respect to the Sun. It has
arbitrarily been
divided into twenty-four hours. The twenty-four hour division
has led to a very practical geographical division of the
Earth into twenty-four zones, east and west, called time
zones. The rotating Earth causes the Sun to appear to move
westward, covering one time zone each hour. North-south
lines, called standard meridians, are described as passing
centrally through each time zone. The standard meridians
do not form the boundaries of the zones, but the boundaries
lie half-way between these meridians. For political
convenience, the boundaries of the time zones are often
distorted east or west to include neighboring communities
within the same time zone.
During the period of British maritime dominance,
the zero, or prime meridian was designated as passing
through the observatory at Greenwich, England. The
standard meridians then are numbered east and west from
there to the one on the opposite side of the Earth, called
the international date line.
The system is fundamentally sound, for it permits
travel throughout the world under standardized time
conditions. All clocks within a time zone read the same
under these standardized time conditions and that time is
called the standard time of that zone. When one moves from
one time zone to an adjacent one, the time must be changed
by a full hour. If there were no time zones, as was once
the case, each community would set its own time based on
the passage of the Sun at that particular location. This,
of course, led to a great deal of confusion until time
zones were agreed upon. The need for such standardization
occurred with the development of the railroads which quickly
spanned the continents.
|
