On this image of the Earth, the horizontal (blue) lines represent lines of latitude and the vertical (pink) lines represent lines of longitude. The horizontal gray line represents the equator and the vertical gray line represents the Prime Meridian; both of these lines represent 0 degrees. The North Pole, at the top of the image, is where all of the lines of longitude come together.
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Image Courtesy of Dennis Ward/UCAR
Latitude and Longitude
The most common way to locate points on the surface of the Earth is by using lines on a map or globe called lines of latitude and longitude.
Latitude describes the location of a place north or south of the equator. The North Pole is +90 degrees and the South Pole is -90 degrees. A line connecting all the points with the same latitude value is called a line of latitude.
Longitude describes the location of a place east or west from the Prime Meridian, a line which runs between the poles and through Greenwich, England. Longitude increases as you leave the Prime Meridian (0 degrees) going east (0 to 180 degrees) and decreases as you head west (0 to -180 degrees), until they meet at 180 degrees. Why does the Prime Meridian go through Greenwich, England? It could be anywhere, but in the mid-1800s the Royal Observatory in Greenwich, England was well known for keeping time, and because the time is the same all along that line of longitude, it was decided that the Prime Meridian would go through Greenwich.
Latitude has a big effect on climate because latitude controls how much solar energy a location receives. The tropics, which are places on or near the equator, are warm all year long because they get about the same amount of sunlight during the year. The polar regions, which include places at or near the poles, have a cold climate and don't get much (if any) sunlight on winter days. The area between the tropics and the poles is called the mid-latitudes. The mid-latitudes have several different seasons during the year because the amount of sunlight changes from summer to winter.
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