Time Zones: Their Invention and Implementation
The basic concept of time is really based upon two very specific movements of the Earth: its
rotation on its axis, and its revolution, or orbit, around the sun. Astronomers stationed at the
observatory at Greenwich, England, set the world's atomic clock by the noonday sun. When
the sun has reached its zenith -- or, as it is sometimes known, the sun's meridian -- it is exactly
noon.
Ancient navigators, however, found it very difficult to know their exact location once they
were out of sight of land. It was not until 1714 that a clockmaker, John Harrison, came to
realize that exact time away from the home port could be calculated using the measurement of
longitude with a starting point of the Prime Meridian. From that, ship's captains could
determine their exact location at sea.
The Earth is divided into 24 time zones so that everyone in the world can be on roughly similar schedules (like
noon being roughly when the sun is highest in the sky). The idea to divide the Earth into time zones was
proposed by the Canadian railway planner and engineer Sir Sandford Fleming (1827 - 1915) in the late 1870s.
Time zones were first used in 1883 by railroads in order to standardize their schedules. World time zones were
determined in 1884, at an international conference in Washington, D.C. Each of the 24 world time zones are
about 15 degrees wide and differ by one hour.
Early Time Keeping:
Until about 100 years ago, each city set its clocks to local time -- noon was the time when the Sun was at its
highest in the sky, as viewed from that city. Even neighboring cities needed to set their clocks differently to
make this happen. For example, when it was 8:00 in New York City, it was 8:12 in Boston (because Boston is
about 3 degrees east of New York). Before modern transportation and communication, this difference didn't
really matter.
A Need for Synchronized Schedules:
Once railroads were built, this became very awkward. Train schedules needed to be written using common time
settings that everybody agreed to, so the U.S. railroad companies adopted the idea of time zones. This was soon
extended internationally, with the world being divided into 24 time zones, each one a long strip from North Pole
to South Pole, about 15 degrees of longitude wide. All the people in one time zone would set their clock the
same way (to the local time in the center of the time zone).
24 Hours in a Day and 24 Time Zones:
Since there are 24 hours in a day, dividing the Earth into 24 time zones meant that everybody was using a time
setting very close to their local time -- there's at most about a half-hour difference. So 7:00 am was still in the
morning, 12 noon was still in the middle of the day, and 7:00 pm was still in the evening.
But this was much more convenient than the older system of using local time. Most neighboring cities use the
same time zone settings. Even if two cities are in different time zones, the time settings always differ by a whole
number of hours (1 hour, 2 hours, 3 hours, etc.), making it easy to convert from the time in one time zone to the
time in the other.
Today, most countries use this time zone system. (In a few places, clocks are set to be 15 minutes or 30 minutes
different from the time according to the standardized time zone system.)
The International Date Line:
The prime meridian (zero-degrees longitude) passes through Greenwich, England. Halfway around the world in
the middle of the Pacific Ocean (180 degrees from Greenwich) is the International Date Line (IDL), where the
date changes across the boundary of the time zone. The entire world is on the same date only at the instant when
it is noon in Greenwich, England, and midnight at the IDL. At all other times, there are different dates on each
side of the IDL.
Directions:
After reading and highlighting important information in the above selection, use the passage to
answer the following questions by writing the correct answer in the blank before each question.
____________________
____________________
____________________
1. How many degrees are there in a sphere, around the earth?
a.
1
b.
15
c.
24
d.
360
2. How many time zones are there in the world?
a.
1
b.
15
c.
d.
360
d.
360
24
3. About how many degrees are there in each time zone?
a.
1
b.
15
c.
24
____________________
4. The time in each zone is about how many hours different than the zone to its
east or west?
a.
1
b.
15
c.
24
d.
360
____________________
5. Fill in the blank with the word that best completes the sentence: latitude or
longitude. Time zones are determined by bands of ________________ ?
____________________
6. Time zones were created to standardize time so it would be easier for everyone
to follow ____________?
a.
School Schedules
c.
The Work Day Schedule
b.
Plane Schedules
d.
Train Schedules
____________________
7. What time of day is it when the sun is at its highest point overhead?
a.
9:00am
b. 12 noon
c. 9:00 pm
d. 12:00 am
____________________
8. Fill in the blank with the word that best completes the following sentence:
Prime Meridian or International Dateline.
"Home port" for time upon which other time zones are based in where the
_________________ passes through Greenwich, England.
____________________
9. Fill in the blank with the answer that best completes the following sentence:
Prime Meridian or International Dateline.
A new day being when the sun crosses the ______________.
____________________
10. True or False?
The time in each zone is one hour earlier than the zone to its east.
____________________
11. Fill in the blank with the answer that best completes the sentence: earlier or
later. If you are in Boston, it is ________________ in London, England which
is to the east of Boston?
____________________
12. Fill in the blank with the answer that best completes the sentence: earlier or
later. If you are in Boston, it is ________________ in Los Angeles, CA which
is to the west of Boston?