EARTH AND SPACE
SCIENCE
Chapter 3 Models of the Earth
3.1 Finding Locations on Earth
3.1 Finding Locations on Earth
Objectives
• Distinguish between latitude and
longitude.
• Explain how latitude and longitude can
be used to locate places on Earth’s
surface.
• Explain how a magnetic compass can be
used to find directions on Earth’s
surface.
Introduction
• Since Earth is a sphere, there is no top, sides,
or bottom to use as reference points for finding
location.
• To solve this problem, Earth’s axis of rotation
is used to establish reference points.
• The reference points established where the
axis transcends the Earth’s surface are the
North and South geographic poles.
• The equator, a circle between the poles,
divides the Earth into the Northern and
Southern hemispheres.
Latitude
• Lines of latitude
can be thought of
as a set of parallel
circles used to
describe positions
north and south of
the equator.
• Lines of latitude
run east and west.
• Latitude is the
angular distance
north or south of
the equator.
Latitude
• Latitude is measured in degrees.
• The distance from the equator to a pole is ¼
that of the circle that would be formed by going
all the way around the Earth.
• The Earth, being a sphere, is 360° all the way
around, so ¼ of that would be 90°.
• Each pole is 90° latitude in its respective
hemisphere.
• Each degree of latitude is about 111 km
(1/360th of the Earth’s diameter).
Latitude
• Each degree of latitude consists of 60
equal parts called minutes (‘).
• Each minute of latitude is equal to 1.85
km.
• Each minute of latitude is divided into 60
equal parts called seconds (“).
Longitude
• East-west locations
are established by
using meridians,
semicircles that run
from pole to pole
along the curvature
of the Earth.
• Prime meridian (0°
longitude) is located
in Greenwich,
England.
Longitude
• The circumference of the world is 360°, so half way
around the world is 180°.
• All locations west of the prime meridian have
longitudes between 0°and 180° west and locations
east of the prime meridian have longitudes between
0°and 180° east.
• Lines of longitude are not parallel, they are farthest
apart at the equator (about 111 km) and get closer
toward the poles.
• Exact locations on the surface of Earth can be stated
with a latitude and longitude, such as Oneonta High
School at 33°56’02”N 86°29’47”W.
Great Circles
• A great circle is any circle that divides the
globe into halves, or marks the circumference
of the globe.
• Great circles are often used for navigation,
especially by long-distance aircraft.
• Great circles can run in any direction around
the globe.
• The route along a great circle is the shortest
distance between the two widely spaced
points.
Finding Direction
• A magnetic compass may be used to find direction
on Earth due to the Earth’s magnetic field.
• The geographic poles are located in different
places than the Earth’s geomagnetic poles.
• Magnetic declination is the angle between the
direction of the geographic pole and the direction
in which the compass needle points.
• Magnetic declination has been determined for
points all over the Earth.
• The magnetic declination for points all over the
globe are changing because the Earth’s magnetic
field is constantly changing.
Finding Direction
• When a person uses a compass, it is important to
figure in the magnetic declination to determine
geographic north.
• Determining geographic north is important in
mapmaking and navigation.
• Global positioning system (GPS) is a satellite
navigation system that is based on a global network of
24 satellites that transmit radio signals to Earth’s
surface.
• A GPS receiver uses signals from three satellites to
determine latitude, longitude, and elevation.
• Personal GPS receivers are accurate up to 10 to 15
meters.
Magnetic Declination
References
• Latitude http://www.lakelandsd.com/tutorial/lesson1.html
• Longitude http://www.lakelandsd.com/tutorial/lesson1.html
• Great Circles http://www.pilotsweb.com/navigate/coordi.htm
• Greenwich, England http://www.discountcityhotels.com/London/Inf
o/London-Sights.htm
References
• Magnetic Declination Map http://user.netonecom.net/~swordman/craft
s/AmateurSurveying.htm
• GPS Illustration http://www.veron.nl/afd/woerden/art/gps_ca
libratie.htm
• GPS Magellan - http://www.hikingsite.nl/gpskoopgids/gps_koopgids_ontvanger.php/ma
gellan_gps310