• Identify what time zone we live in
• Given a city calculate the time in that specific
time zone based on the time in Pensacola, FL
• Explain how time zones are divided (15 degrees
per time zone 15/360 = 24 time zones)
• Identify where Greenwich Mean Time is located
• Identify where the International Date Line is
located
Areas of the Earth divided into
15 degree zones that share the
same time.
World Time Zones
The time zone that the prime meridian
is located in. Named after Greenwich,
England where the imaginary line runs
through
An imaginary line on the surface of the Earth
running north to south and separates one calendar
day from the next. This is located in the Pacific
Ocean at longitude line 180 degrees.
Introduction
The Earth is currently divided into
24 major time zones so that everyone
in the world can be on roughly similar
schedules (noon being roughly when
the sun is highest in the sky).
What are time zones?
• We have time zones in order for people to
take the best advantage of daylight hours.
• The Earth is almost a perfect sphere and
has a 360 degrees
• Each time zone is 15 degrees
• Total of 24 Time Zones
We measure the day by saying that the
sun is at it's highest point at 12 o'clock,
midday. Because the earth spins, as it
travels around the sun, one half of the
earth is in darkness and one half in light,
all the time. This brings us to a problem.
If it is midday where you are, on the
opposite side of the earth, it is dark, so
what time is it on the opposite side of the
world?
HOMEWORK ASSIGNMENT
Students will:
Determine what time it in the following cities if
it is 4pm in Pensacola, FL
(*Hint use the time zone map on the resource page).
- New York City, NY
- Paris, France
- Moscow, Russia
- Sidney, Australia
- Rome, Italy
Before time keeping and clocks were invented, people used to know approximately what
time it was by watching the sun. If you look out of the window, at different times of the
day, you will see that the sun is in a different place each time you look. This is the same
everywhere in the world. Once clocks were invented, they simply had to look at a clock to
know what time it was. The earth spins on an imaginary line known as its axis, this
movement is known as rotation. While it is rotating on its axis, it is also traveling around
the sun, this movement is known as revolution. Although the earth is revolving around the
sun, the sunlight only falls on the part of the earth facing the sun. So, the part facing
the sun has day and the part away from the sun has night. As the earth rotates different
parts are exposed to the sun, and put in the shade.
There are 360 degrees of longitude on the earth, so what the scientists did was divide
these by 24, that means that there are 15 degrees of longitude in every time zone. If
you travel more than that, you have to adjust your watch. You may be wondering why time
zones are measured in degrees of longitude and not miles or kilometers.
Who came up with the idea of time zones?
The idea to divide the Earth into time zones
was proposed by the Canadian railway planner
And engineer Sir Sanford Fleming (1827 1915)
in the 1870’s.
When were time zones first used?
• Time zones were first used on November
18, 1883 by railroads in order to make
their schedules less confusing.
• 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 each city.
Neighboring cities needed to set their clocks
differently.
• For Example, when it was 8:00 in New York City, it
was 8:12 in Boston (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.
How to Calculate Time Zones
How to Calculate Time Zones
In order to calculate time zones one
should first determine what time zone they are
in. For example Pensacola, FL is in the United
States Central Time Zone (which is six time
zones west of GMT or Time Zone 0 and is
represented on the map on the previous slide by
-6).
Next determine the location you wish to find out what time it is.
Locate it on the previous map. For Example Naples Italy is in Time
Zone +1 of Greenwich Mean Time (GMT Time Zone 0). Simply count
the time zones between the two places and add that many time zones if
you count to the east or subtract the number of time zones if you count
to the west. The difference between -6 time zone (United States
Central Time) and +1 time zone (Naples, Italy) is 7 time zones to the
east which means you would add 7 hours to determine the time difference
between Pensacola, FL and Naples, Italy. So if it is 1pm in Pensacola,
FL it is 8pm in Naples, Italy.