Frame of Reference

# Frame of Reference - The Frame of Reference: Earth's...

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The Frame of Reference: Earth's Location Grid, Time Zones, and the International Date Line LATITUDE AND LONGITUDE Because Earth's surface is vast and complex. we need a uniform system for identifying locations, especially locations relative to other places. On a sphere like the Earth, directions like "north" or "wesf' have no meaning unless everyone agrees on a starting point to which they can refer. After all, if you head "north" and continue far enough in a straight line, you eventually will cross the North Pole and find yourself heading south! Maintaining a course in the constant direction "easr' eventually will bring you back to the starting point; in fact, you would come back to your starting point from the west! Earth rotates about an axis, an imaginary line connecting the poles of rotation. At the poles themselves, theoretically there is no motion of rotation at all because the rest of the surface rotates around the poles. These two poles, north and south, provide natural reference points. They make it possible to determine the Equator, the line connecting all points on the globe that are exactly "equally distant from" or halfway between the North and South Poles (Figure 2-1). The Equator divides Earth into two half-spheres, or hemispheres, a Northern Hemisphere and a Southern Hemisphere. We use the Equator as the starting point in identifying locations on a north-south basis. Any point not on the Equator must be either north of it or south of it. On Earth, the farthest north you can get from the Equator is one- quarter of a circle. One-quarter of a 360 degree circle is 90 degrees. So, the North Pole is 90 degrees north of the Equator and the South Pole is 90 degrees south of the Equator. Because the poles are points, not lines, we need no further location information other than "90 degrees N" or "90 degrees 5" to state the precise location of either pole. (Continuing in a straight line from the Equator for more than one- quarter of a circle would carry you beyond the North Pole, and thus you would be heading southward.) But what if the location of a place is halfway between the Equator and the North Pole? The place would be at 45 degrees N latitude. However, 45 degrees N latitude is more than one place; it is a line connecting al/ the points around the globe that are halfway between the Equator and the North Pole. For example, Salem, Oregon, is close to 45 degrees N. So are Bordeaux, France: Torino, Italy; and Harbin, China. Obviously, knowing that a place is "45 degrees N" is not enough information to pinpoint its location! It is like being told that your seat in a huge stadium was in the fifth row. Where in the fifth row would be your next question! So, how can we specify an east-west

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## This note was uploaded on 04/22/2008 for the course SOC 321 taught by Professor Reiter during the Fall '08 term at Ohio State.

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Frame of Reference - The Frame of Reference: Earth's...

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