Mapping_the_Earth1.ppt

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Mapping the Earth

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How do we know the Earth is not

flat

?

• EVIDENCE FOR EARTH’S SPHERICAL SHAPE

– Ships appear to “sink” as they approach the horizon – Other celestial objects are round.

– Now we can see earth from space, and photograph it! • BUT, the most important proof that Earth is round is the

fact that the altitude of Polaris increases as you move toward the North pole, or decreases as you move

toward the equator!

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EARTH’S SHAPE

• Of course, Earth is not perfectly

spherical…

• What is the exact shape of the

Earth?

NOT THIS! NOT THIS EITHER – BUT CLOSE! NOT THIS!

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• This is a more

realistic view of Earth • It’s not really as

“oblate” or oval as I drew it on the

previous slide

• But it’s still an oblate

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Why Maps?

For thousands of years, people have used maps

to define borders and to find places.

 CartographyCartography is the science of mapmaking. is the science of mapmaking.

 Cartographers use an Cartographers use an imaginaryimaginary grid of parallel lines grid of parallel lines

and vertical lines to locate points on Earth.

 The The equatorequator circles Earth halfway between the circles Earth halfway between the

north and south poles separating Earth into two

equal

equal halves called the northern hemisphere and halves called the northern hemisphere and the southern hemisphere.

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Latitude

• Parallels

- imaginary circles running east/

west on the globe; determine how far

north/south one is; named because they

parallel the equator

• Latitude

- the angular distance from north

and south of the Equator; measured in

degrees (90° intervals)

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Latitude

• Latitude is thus measured from 0° at the equator to 90° at the poles.

• Locations north of the equator are referred to by degrees north

latitude (N).

• _{Locations south of the} equator are referred to by degrees south

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BASED ON THE ____________

OF _______________

Demo

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Longitude

• Meridians - lines running north/south on the globe, pole to pole; determine how far

east/west one is

• Prime Meridian- the point 0° longitude; runs through Greenwich, England

• Longitude- the angular distance east or west of the Prime Meridian; all measured from 0°- 180° east or west of the Prime Meridian

– Longitudinal Great Circles- any two meridians

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Longitude

• Points west of the

prime meridian are numbered from 0° to 180° west longitude (W).

• Points east of the prime meridian are numbered from 0° to 180° east

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– _{Both latitude and longitude} are needed to precisely

locate positions on Earth. – For example, the location

of New Orleans is: 29°57 ´N, 90°04´W.

– Note that latitude comes first in reference to the coordinates of a

particular location.

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Let’s do

some

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Assessment

Match the following terms with their definitions.

___ latitude ___ longitude

___ prime meridian ___ equator

A. the reference point for longitude

B. the distance in degrees east or west of 0°

C. the reference point for latitude

D. the distance in degrees north or south of 0°

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_______ A degree of longitude always represents the

same distance.

_______ If you travel west across the International Date Line, you advance your calendar one day.

_______ Lines of latitude are not perfectly parallel to each other.

Assessment

Identify whether the following statements are true or false.

false

true

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EACH HOUR,

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Example: Two students record a

difference in local time of two

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Direction Finding

• Geomagnetic Poles- the point above the earths poles where all magnetic lines

converge;

– The earth behaves as a giant magnet with areas near the north and south pole acting as the ends of the magnet; this affects compasses different amounts in different areas

• _{Magnetic Declination-}_{the angle between the} direction of the earth’s geographic pole and the direction in which a compass needle points