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/Info/London-Sights.htm

References

• Magnetic Declination Map - http://user.netonecom.net/~swordman/crafts/AmateurSurveying.htm

• GPS Illustration - http://www.veron.nl/afd/woerden/art/gps_calibratie.htm

• GPS Magellan - http://www.hiking-site.nl/gps-koopgids/gps_koopgids_ontvanger.php/magellan_gps310