LONGITUDE
By
Chris Pelletier
copyright 2010
When you look at a globe or a map, you can see lines going up and down, as well as side to side. They make a grid pattern which helps to locate things on Earth. The lines going from east to west are called lines of latitude (or parallels). The lines running north and south are called lines of longitude. Both are very important to know for travel by ship, airplane and even cars. People use the lines for navigation, or steering your course.
In ancient Egypt, Aristophanes, a Greek mathematician and philosopher living in Alexandria, heard stories of how a well at noon showed the sun directly in it, but a well in a different city cast a shadow on the same day. So Aristophanes hired a man to walk from one city to another on a north-south axis. Using the information of distance, he calculated that the earth was round and was accurate in figuring its circumference. He was just off by a couple of thousands of kilometers. It was quite a feat for ancient times.
Sailors over the centuries used that knowledge and the stars to help get around. Using the stars to steer is an art still alive today called celestial navigation. Before modern times and GPS devices, though, sailors could determine how far north or south they were of the equator without much difficulty. However, figuring out how far west and east eluded them due to the inability to measure time. If one looks at 17th century sailing charts, there are many diagonal to steer by. And those were rough estimates.
That inability hindered determining longitude, and England offered a huge prize for an inventor who could come up with a working marine chronometer (clock). The task was daunting, due to the motion of the ocean, and many people tried. In 1735, a carpenter named John Harrison submitted a chronometer which held up to the rigors of the sea. From then on, nautical charts and navigation made shipping easier and safer.
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