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9
PENNSVALLEY
Lesson 3: (Cont.)
Earth’s Time Zones and
the International Date Line
Part B –Calendar DayChanges onEarth
Let’sdive into timea littledeeper.Linesof longitude, ormeridians, divide theearth into theWestern
and Eastern Hemispheres. Recall that the PrimeMeridian is 0° longitude. Halfway around the world,
or the other side of thePrimeMeridian, lies the 180°meridian.This line is known as the International
Date Line (IDL).
It is at this line, the 180th, that the calendar day changes.A new day has to
begin somewhere on earth. That new day begins at the International Date
Line.Travelingwest, if it isThursdayat the179°west longitude line, it isFriday
at the 179° east longitude line.The new day begins once you cross the 180th
line of longitude travelingwest.
An example of how the calendar day changeswhen traveling around the earth
wouldbehelpful. If you leaveFriday fromPhiladelphiaand travel west onaplane,
it is alreadySaturday inSydney, Australia.Sydney is across the International DateLine.
Here is a “rule of thumb” to remember when traveling the globe.You will set your calendar ahead
(+) one day going west across the Date Line.You will set your calendar back (-) one day going east
across theDate Line.
ACTIVITY:
Use the information in this lesson to answer the following questions.
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1.Howmany time zones aremapped out on earth?
____________________
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2.Howmany degrees are there in each time zone?
____________________
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3.Howmany degrees are in a sphere?
____________________
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4.Howmany time zones and hoursmake up theEasternHemisphere? ____________________
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5. Travelingwest, when it is Friday inPennsylvania, what
day is it inAustralia?
____________________
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6. Traveling east, when it isWednesday inAustralia, what
day is it inPennsylvania?
____________________
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7.When traveling east across the IDL, does one add or
subtract a day from his/her calendar?
____________________
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8.When travelingwest across the IDL, does one add or
subtract a day from his/her calendar?
____________________
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9. If it is 12:00 noon at thePrimeMeridian, what time is
it seven time zones to thewest?
____________________
10. If it is 4:00 pm inNewYork, what time is it four zones to the east?
____________________
11. If it is 3:00 pm inPhiladelphia, what time is it five
time zones to thewest?
____________________
179° E
179°W
Saturday
Friday
180° IDL
Geography Skills
