Time Zones
• As a very general rule of thumb, in the past people use to keep track of
time by looking at the position of the sun overhead. When it was directly
overhead they referred to this as “High Noon” or 12 o’clock noon.
• In the 19th century With the advent of rapid travel by trains and
improvements in communication, it became necessary to standardize the
time for all cities within a certain region. (Because not all cities in a region
would have the sun directly overhead at the same time).
• In November 1883, the railroad companies divided the United States
into four time zones.
– Everyone in a time zone set their clocks to the same standard time.
• In 1884, an international conference was held in Washington D.C.
by 26 countries. At this meeting they divided the world into 24 times
zones, with each zone being roughly 15 degrees wide in longitude.
• Since there are 24 hours in a day, and 360/15=24, the time in each zone
differs from the time in adjacent zones by one hour.
• Time zones have been modified for political, social and economic reasons.
Time Zones
Æ 24 time zones on the Earth’s surface
[each one covers 15° (360° circum. / 24 hours in a day = 15°)]
Standard Time
Æ Beginning of November to the Beginning of March
Shown below are the Time Zones that you are responsible for. The sample times listed are for Standard Time.
HawaiiAleutian
Standard
Time Zone
9 am
Alaskan
Pacific
Mountain
Central
Eastern
Atlantic
Standard
Time Zone
Standard
Time Zone
Standard
Time Zone
Standard
Time Zone
Standard
Time Zone
Standard
Time Zone
10 am
11 am
12 noon
1 pm
2 pm
3 pm
Daylight Saving Time ÆÆÆ Beginning of March to the End of October
We turn our clocks 1 hour ahead of standard time in March (Spring Forward)
We turn our clocks 1 hour back to standard time in November (Fall Back)
(Not everyone uses it in the U.S. Æ Arizona and Hawaii do not use it)
Shown below are the Time Zones that you are responsible for. The sample times listed are for Daylight Saving Time.
HawaiiAleutian
HawaiiAleutian
Hawaii
D.S.T.
Time Zone
Standard Time
9 am
10 am
Hawaii does not use
Daylight Saving Time,
but the Aleutian
Islands do use it.
(see above)
Alaskan
Pacific
D.S.T.
Time Zone
D.S.T.
Time Zone
11 am
12 noon
Mountain
D.S.T.
Time Zone
Central
Eastern
Atlantic
D.S.T.
Time Zone
D.S.T.
Time Zone
D.S.T.
Time Zone
2 pm
3 pm
4 pm
1 pm
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In Arizona it
would be 12 noon
Arizona does not
use Daylight
Saving Time.
(They stay on
Standard time)
Jet Lag – The combination of exhaustion, irritability, and insomnia
that travelers often suffer after a long flight across several time zones
See the maps on the next page for a real world application.
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International Date Line
– Imaginary line running from north to south through the Pacific Ocean.
-- The point in the time zones where the date changes from one day to the next.
– As you go from east to west, you gain
a day as you cross the line.
– As you go from west to east, you lose
a day as you cross the line.