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PENNSVALLEY
Lesson 4: (cont.)
HowDoWe Use Lines of Latitude and Longitude?
Part 2 – Longitude
Now it is time to switch directions! Remember the other lines that crisscross parallels are called
meridians
.Remember thatmeridians have lines that runnorthand southbutmeasuredistances east
and west in degrees called longitude. Meridians have a different story to tell. These lines are not
parallel, and they come together at the geographic poles.
Remember the starting point for parallel lines is the Equator.Well, we need a starting point for
meridians as well. That starting point is called the
Prime Meridian
at 0 degrees longitude. That line
runs through theUnitedKingdom, or Great Britain.Because the earth is a sphere, and there are 360°
in a sphere (circle if on flat paper), meridians range from 0 degrees to 180°.That is truewhether you
are going east or west. Starting at 0 degrees longitude and heading east to 180° longitude, all of the
area between these twomeridians is known as theEasternHemisphere.
Let’s go back to thePrimeMeridian.This time, if we headwest, we have the same range— only
from0° to180°W, or 180degreeswest longitude.Thisarea isknownas theWesternHemisphere.Add
180 degrees to 180 degrees and you have a 360° sphere, or the earth.
Part 3 –Time Zones
Meridians serve another important function.We cannot have the same time all over the earth!
They provide us with our
time zones.
Every time zone is divided into about 15 degrees. It takes the
sun’s raysabout onehour to cross15degrees (remember dayandnight).Let’sdoa simplemathprob-
lem. And howmuch does 15° times 24 equal?
That’s howmany degrees arearounda sphere.
Howmany hours are in our planet’s day?
That should equal the number of time zones we
have on earth.
When travelers enter a new time zone headedwest, theymove their clocks back one hour!When
travelers enter a new time zone headed east, they set their clocks ahead one hour!
Entering a new time zone headedwest,
turn your clock back one hour.
Entering a new time zone headed east,
turn your clock aheadone hour.
Geography Skills
