Location, Location, Location

Geodesy The study of the size and shape of the Earth.

The Earth is… 3000 BC Babalonians An oyster 600 BC Greeks Flat 500 BC a perfect shape A sphere 300 BC Circumference ~ 25,000 miles, Dark ages Flat again 1492 Columbus A pear 1753 French Oblate ellipsoid Spheriod Geoid to describe the deviations from a spheriod

The Earth as a Geoid

Geographic Coordinate System Parallels Meridians Great and Small Circles

Geographic Coordinate System GCS uses a 3-D spherical surface to define locations on Earth. GCS includes an angular unit of measure, a prime meridian and a datum.

Locating yourself on a Sphere You need a frame of reference That is the purpose of Latitude and Longitude Defining these parameters: Earth rotates on an imaginary axis ~ North and South Poles Equator: is a great circle that lies equidistant between them.

Great Circles ..are imaginary circles of the surface of the earth who's plane passes through the center of the earth.   The circumference of the earth is 25,000 miles or 40,000 km "Great" because it is the largest possible circle

Great Circles: Cut the earth in half and each half is known as a hemisphere Are the circumference of the earth Provide the shortest routes of travel on the earth's surface. ** Planes travel in great circles. ** We were always taught a line is the shortest distance between two points - Not True. Small circles: circles whose planes do not pass through the center of the earth.

Latitude Latitude: is the angular distance north or south of the equator. (0 –90 degrees N or S) 1° of latitude = 40,000 km/ 360° 1 degree = 60 minutes 1 minute = 60 seconds 36°49'52" N ArcView 3.x uses Decimal Degrees only Sextant measures the angular distance between 2 points (sun & horizon) **So it easy to determine latitude.

Longitude: Longitude: no natural reference point In 1884 by International Agreement Greenwich England was the chosen starting point. This is called the prime meridian or zero degrees and everything is east or west of that. Longitude is the angular distance east or west from Greenwich, England (0 – 180 degrees E or W)

Geographic Coordinate System Longitude and Latitude Degrees, minutes, seconds 1o latitude ~110.5 km (equator) 1o longitude = cosine of the latitude 1 minute of latitude ~1852 m

How to convert from DMS to DD Example: 37°36’30” Divide each value by the number of minutes or seconds in a degree 36 minutes = .60 degrees (36/60) 30 seconds = .00833 degree (30/3600) Add it all up 37° + .60 + .00833 = 37.60833 DD

The global grid: Parallels: lines of latitude, only the equator is a great circle all other parallels are small circles (they never meet) Meridians: these are line of longitude and when joined with its mate half way around the globe form great circles * the distance between meridians will vary with latitude

How the Earth is Divided Hemispheres: Northern, Southern, Eastern, Western

Time Zones Solar noon: most towns used this, defined as when a vertical stake cast the shortest shadow. By the 19th century transportation and communications (namely railroads and telegraph) connected towns and cities, the adopt of a standard time was necessary.

Time Zones (continued) 1884 at the International Meridian Conference 24 time zones were established. Greenwich Mean Time (GMT) = Universal time = Zulu time 360°/24 = 15° for each time zone, however for convenience many time zones follow state and country lines. International Date Line: where each new day begins 180th meridian Chronometer  

Time Zones