Geography Reference
In-Depth Information
pines, it is 1
A.M.
and the next day has begun. In Tokyo, nine time zones earlier, it is 2
A.M.
and in Mel-
bourne, Australia, it is 3
A.M.
the next day.
At points west of London, in South America and North America, it is earlier in the day. At 5
P.M.
Lon-
don time, it is 2
P.M.
in Rio de Janeiro; 12 noon in New York City and Quebec; 9
A.M.
in San Francisco and
Vancouver, Canada. Way out in Anchorage, Alaska, it is 8
A.M.
While this gave the world a uniform clock, it raised another question: where does one day turn into
another? The logic behind this question is simple. Twelve time zones to the west from London, it is twelve
hours earlier. Twelve time zones to the east, it is twelve hours later. One place can't be both.
For example, if it is 5
P.M.
on Sunday in London, it is twelve hours later to the east, or 5
A.M.
on Monday.
Yet at the same time, it is twelve hours earlier to the west, or 5
A.M.,
on Sunday. But how can it be two dif-
ferent days in the same place? The simple solution was to establish another of geography's imaginary lines
on the meridian of 180˚, directly opposite the prime meridian at Greenwich. This is where East literally
meets West. In 1883 this line became known as the international date line, the point at which the calendar
day changes by one day as it is crossed. Fortunately, this line happens to be in the middle of the Pacific
Ocean (for the most part), where it can cause the least confusion. The date line does zigzag its way around
several spots to keep some places within the same time zone.
In practical terms, the date is one day earlier on the eastern side of the line; and it is one day later on the
western side of the line. A traveler crossing the date line westward advances the calendar—for example, 5
A.M.
Sunday becomes 5
A.M.
Monday. A traveler crossing the date line eastward has to put back the calen-
dar from 5
A.M.
Monday to 5
A.M.
Sunday. Depending on which side of the date line the traveler is on, he
is now twelve hours different from London, either earlier or later.
What Does the Continental Divide Divide?
Let's start by explaining what it doesn't divide. A continental divide does not cut continents into equal
pieces. One of those invisible boundaries that geographers find so useful, a continental divide is a line of
high mountain peaks marking the point where a continent's rivers begin to flow in opposite directions. As
the water flows down one side of the range or the other, its ultimate destination is set. In North America,
it is a ridge of high ground running irregularly through the Rocky Mountains and Mexico's Sierra Madre,
and separating eastward- from westward-flowing streams. The waters that flow eastward empty into the
Atlantic Ocean, chiefly by way of the Gulf of Mexico; those that flow westward primarily empty into the
Pacific, although some drain into the deserts of the Southwest and never reach the ocean.
Each of the continents has a similar mountain range or high ridge that directs the flow of rivers in op-
posite directions. In South America, the continental divide follows the course of the Andes, and rivers flow
either to the Pacific or, like the Amazon, into the Atlantic. Europe's divide separates those streams that
drain into the Atlantic and Arctic Oceans from those that flow into the Mediterranean and Black seas. In
Asia, the divide separates rivers that flow into the Indian Ocean, including the Ganges and Indus, from
those that empty into the Arctic and Pacific Oceans. Africa's divide separates streams that drain into the
Indian Ocean on the east and the Atlantic on the west. And in Australia, the continental divide separates
Pacific-draining rivers from waters that empty into the Indian Ocean.
Geographic Voices
Meriwether Lewis, from
The Journals of Lewis and Clark
11th. February Monday 1805.
