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Latitude and Longitude. Coordinate Systems. When you are locating a point on a flat surface you can use Cartesian coordinates of x and y. The point 2, 3 is plotted on the graph. y-axis. x-axis. Coordinate Systems.
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Latitude and Longitude PSC 121 Prince George’s Community College Barbara Gage
Coordinate Systems • When you are locating a point on a flat surface you can use Cartesian coordinates of x and y. • The point 2, 3 is plotted on the graph. y-axis x-axis
Coordinate Systems • On a body such as the Earth or our moon, we can pinpoint the location of any city or landmark using two values, the latitude and longitude. These are polar coordinates.
On the Earth there are two additional sets of reference points. • The Equator divides the Earth into the Northern Hemisphere and the Southern Hemisphere. http://nationalatlas.gov/articles/mapping/IMAGES/latlong2.gif
The Prime Meridian divides the Earth into the Western Hemisphere and the Eastern Hemisphere. http://www.arcticice.org/images/long.gif
Latitude • Latitude is defined as the elevation of the location point above (or below) the equator. • The measurement is expressed in degrees, minutes, and seconds. • The equator is at 0° and the poles are at 90°. http://webhelp.esri.com/arcgisdesktop/9.2/published_images/LatLong%20from%20Globe%20Center.gif
Latitude • If the location point is north of the equator an N or + is added to the degrees. • If the point is to the south of the equator an S or – is added to the value. 52°N or +52° 24°S or -24°
Latitude • On the Earth we designate lines of equal latitude as parallels. http://www.lakelandsd.com/tutorial/latitude2.jpg
Longitude • Longitude is defined as the measurement of the location point east or west of the Prime Meridian • The value is also expressed in degrees, minutes, and seconds. Note: There are 60 minutes in a degree and 60 seconds in a minute.
Longitude • If the point is located to the west of the Prime Meridian we add a W to the value. • If the point is located east of the Prime Meridian we add an E after the value 30°W 80°E
Longitude • On the Earth we designate lines of equal longitude as meridians. • The Prime Meridian has a value of 0° and no E or W. The longitude values increase up to 180° in both directions. http://www.lakelandsd.com/tutorial/latitude2.jpg
Longitude and Time • Local noon poses a problem for travelers because it is noon at different times in different locations. That means that timetables are useless. • To solve this problem time has been gauged from the Prime Meridian also called the Greenwich Meridian (since it passes through the Royal Observatory in Greenwich, England).
Longitude and Time • If you place meridians 15° apart starting with the Prime Meridian, you will divide the Earth into 24 zones. These correspond to the 24 hours in a day. http://www.mapsofworld.com/time-zone-map/maps/world-time-zone.jpg
Longitude and Time • As you travel around the world to the east, you gain an hour in time for each zone you cross. If you travel to the west you lose an hour. http://www.astro.ufl.edu/~oliver/ast3722/lectures/CoordsNtime/timezon2.gif
But… • If you traveled around the world to the east fast enough you would be a day older in a short time! • If you traveled west you could go back in the past! • To solve this problem it was agreed that the 180° meridian would signal the change of date point. • Travel east and the date goes back one day; travel west and you advance a day when crossing this meridian.
But… • To keep all of a country in the same time zone, the International Date Line does not follow the 180° meridian exactly. • Other time zones make the same accommodations for country or state boundaries.
