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 (1/360 th 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 Longitude Great Circles Greenwich, England - o/London-Sights.htm o/London-Sights.htm

References Magnetic Declination Map - s/AmateurSurveying.htm s/AmateurSurveying.htm GPS Illustration - libratie.htm libratie.htm GPS Magellan - site.nl/gps- koopgids/gps_koopgids_ontvanger.php/ma gellan_gps310http:// site.nl/gps- koopgids/gps_koopgids_ontvanger.php/ma gellan_gps310