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.
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