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Earth Sense: Latitude, longitude and the International Date Line
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The global coordinates you can get with a GPS or smartphone can be confusing. Their units are degrees, minutes and seconds of angle. With exact coordinates, you can pinpoint any place in the world. For example, 34 degrees 18 minutes 14.29 seconds north by 83 degrees 49 minutes 35.44 seconds west gets you to the home of The Times.

Why is it so complicated, instead of just squares? It’s because we’re located on a rotating ball, not a flat surface. The first set of numbers, called latitude, indicates an angle from the equator (the “waistline” of the globe). It ranges between zero, which is the equator, and 90 degrees. Ninety degrees north is the North Pole. So Gainesville is about one-third of the way from the equator to the pole.

The second measure is at a right angle to it. There’s no natural reference point, so it was established by international convention to use the line that connects the North and South poles and passes through Greenwich, United Kingdom. Like slicing an orange, we then go around the globe in both directions, measuring degrees of angle called longitude.

After crossing a little over 84 degrees west of England, we arrive in Gainesville. Going 84 degrees in the opposite direction, at the same latitude, would take us into the Tibetan Plateau of China, north of the Himalaya Mountains.

Longitude isn’t limited to 90 degrees. Two travelers could go west and east, until they meet again on the other side of the globe. Each will have completed a half-circle, or 180 degrees, so that’s the maximum longitude. The system was set up to have the 180-degree line in the middle of nowhere, near the center of the Pacific Ocean.

The reason is that something weird happens here. All places on the same longitude line (or “meridian”) have the same clock time. When you travel west, like flying from Atlanta to Los Angeles, the time zones get earlier and earlier. But you can’t go around the globe and arrive 24 hours before you even started. So at 180 degrees longitude, the calendar snaps forward by one day, if you keep going west. You still set your watch to an earlier time, but now it’s Monday instead of Sunday.

If this happened in the middle of Gainesville, the effect would be massive confusion. So the International Date Line was deliberately placed in the Pacific, far away from where most people live.

Rudi Kiefer, Ph.D., is a professor of physical science and director of sustainability at Brenau University. His column appears Sundays and at gainesvilletimes.com.

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