Locating Positions on Earth

Coordinate Systems

A coordinate system is a method of locating a

position on a 2-dimensional surface using two numbers

(called coordinates).

Earth scientists use the latitude-longitude

coordinate system to identify locations on Earth’s

surface. Latitudes and longitudes are measured in degrees (°) and minutes (‘). Each degree (°) is made up

of 60 minutes (‘).Sydney,

Australia = 34°0’S, 151°0’E

Latitude

Latitude is the angular

measurement north or south of the

equator.

The equator (0°) marks the middle of the Earth –halfway between the North and South poles.

Parallels = lines of latitude that

“parallel” that of the equator.

Latitude

The latitude of any point on the Earth

is the angular measurement between the

location and the equator using the center of the Earth

as a focal point.

Latitude measurements above the equator are referenced with an “N”

for Northern Hemisphere.

Latitude measurements below the equator are referenced with an “S”

for Southern Hemisphere.

Measuring Latitude

Scientists may use the position of stars in the night sky to determine the latitude of their position on the Earth’s surface.

Polaris (The North Star) is seen by observers in the Northern Hemisphere. The star is positioned in the night sky

nearly directly over the North Pole.

By measuring the angle between an observer’s view of Polaris and the horizon, one can determine the latitude they are at

in the Northern Hemisphere..

This observer is located at 20°N latitude.

Measuring Latitude

Pointer stars in the “Big Dipper” constellation allow the viewer to find Polaris .

A sextant is an instrument used by an observer to determine the angle

between Polaris and the horizon.

observer

Polaris

horizon

40°

The observer is located at

40° N latitude.

Longitude

Longitude is the angular

measurement east or west of the

prime meridian.

Meridians = “semi-circle” arcs of longitude on the Earth’s surface the connect the North

and South poles.

The prime meridian (0°) marks the middle of the Earth –halfway between the Eastern

and Western Hemispheres.

Longitude

The meridian that passes through

Greenwich, England has been designated as the prime meridian (0°).

The longitude of any location on the Earth’s surface is the number of degrees between the location and that of the

prime meridian.

Longitudes increase east and west from the prime

meridian to the International Date Line (180°)

Longitude measurements

east of the prime meridian are referenced with an “E” for

Eastern Hemisphere.

Longitude measurements

west of the prime meridian are referenced with a “W” for

Western Hemisphere.

Eastern Hemisphere

Western Hemisphere

Measuring Longitude

The longitude of a position on Earth’s surface can be determined if one studies the rate of Earth’s rotation

over time.

The Earth rotates at a rate of 15° per hour from west to

east..

Measuring Longitude

Scientists will use GMT = Greenwich Mean Time as a means by which to gauge the

local time and location of longitude for an

observer.

For example, if the sun has reached its highest altitude in

the sky (local noon – 12 pm) at Greenwich, it will be 11am at 15°

E and 1pm 15°W.

0°12 pm

15°E1 pm

15°W11 am

Remember*** The Earth rotates from

west to east at a rate of 15° per hour.

Measuring Longitude – Sample Problem “If it 6 pm at Greenwich England, at

which location would it be 10 pm?”

B

CA

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