“Don't worry about
the world coming to
an end today. It is
already tomorrow in
Australia.” (Charles
Schultz, creator of
Charlie Brown)
TIME ZONES
WHY DO WE HAVE TIME ZONES?

Since the sun is shining on one part of the
globe while it is dark on another part of the
globe, the earth is divided up into time zones.
This way, if it is noon in Utah, the sun is shining,
but since at that same moment it is dark on the
opposite side of the world, we say it is midnight
there.
THE WORLD IS INTERCONNECTED

Using a time zone map helps us to know what
time it is in any given place. This is especially
important because today the world interacts
with each other more than it ever used to.
HOW MANY TIME ZONES ARE THERE?

The distance around any circle is 360 degrees. Thus
the earth is divided into 360 degrees of longitude.
Since there are 24 hours in a day, each time zone is
equal to 360 (total degrees of longitude) divided
by24 (hours in a day), which gives us 15 (degrees per
hour). In other words, there are approximately 15°
longitude in every time zone and there are 24 time
zones.
IRREGULAR TIME ZONES

In reality, the time zones are not that exact
because each country may modify the
standards to meet its own needs. Additionally,
some areas of the world are on the half hour
(irregular time zones) rather than the full hour
relative to the rest of the world.
INTERNATIONAL DATE LINE

The International Date Line is halfway
around the world from the Prime Meridian
(0° longitude). Therefore, it is at 180°
longitude. The International Date Line is,
by international agreement, where a given
day actually starts. For everyone around
the world, the new day begins at midnight.
But since we are not all having midnight at
the same moment, the world starts the day
in shifts, not all together. Some countries
might be having Wednesday while the rest
of us are still on Tuesday!
INTERNATIONAL DATE LINE

East of the International Date Line is always
one full day “behind” in time. So if it is Sunday
west of the line, it is Monday east of the line.
West of the line is always one day ahead in
time. If it is Tuesday east of the line, it is
Monday west of the line.
FIGURING HOURS

Here is the way to use a time zone map. If you
travel from one time zone to another you either
add or subtract hours from where you start. If you
go east, you add hours. If you go west, you
subtract hours. So, if you started at 8:00pm and
travel west four time zones, you would subtract
four hours and it would be 4:00 pm. If you started
at 8:00 pm and went east six time zones, it would
be 2:00am.
SIMPLIFIED

Simply put, on a time zone map, when you are
going to the right, you add hours. When you
are going to the left, you subtract hours.
FIGURING DAYS

However, if you are going to the right and you
cross the International Date Line, you keep
adding hours, but you subtract a day. If you are
going to the left and you cross the International
Date Line, you keep subtracting hours, but you
add a day.
REVIEW





GOING LEFT
GOING RIGHT
SUBTRACT HOURS if you are going to the LEFT (west)
ADD a DAY if you are going to the LEFT (west) when you
CROSS the International Date Line
ADD HOURS If you are going to the RIGHT (east)


SUBTRACT a DAY if you are going to the RIGHT (east)
when you CROSS the International Date Line