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Margot Dunlap,, age 11, of Pittsburgh, Pennsylvania, for her question:

Who invented the equator?

Suppose you lived on a mid ocean island. You have no books, no maps or charts and no teacher to instruct you. But you happen to be a dedicated star gazer and very, very intelligent. You could, in a few years, figure out the shape of the earth, the positions of the poles and the equator.

The equator, of course, is the midway marker between the North and South Poles. These geographic poles are the two ends of the axis around which the earth rotates once every calendar day. The poles and the equator are the basic markers from which we figure the lines of latitude and longitude. This clever system of coordinates gives the geographic location of every spot on the surface of the globe. You would think that it was invented after mankind had traveled the entire earth from end to end. But this is far, so very far from true.

The clever system dates back thousands of years and the equator was invented at least twice by people who had never traveled far from home. The fantastic story becomes more believable when we remember that mankind is a born star gazer and that the earth's geographical coordinates are based on the motions of the starry heavens. Before the dawn of history, a simple shadow stick was used to point out the north and south, east and west. This useful invention was run by the daily and seasonal motions of the sun.

Early astronomers saw the sky as a vaulted dome, dotted with moving heavenly bodies. They grouped the stars in constellations and observed the dome itself turn completely around every calendar day. The celestial sphere rotated around a northern point marked by the fixed star Polaris. It was natural to section the celestial sphere with lines running north and south, east and west. Directly below these heavenly lines are the earthy lines of  geographical latitude and longitude.

This gives directions, but more was needed to place the equator and early astronomers were limited to the Northern Hemisphere. The Greeks deduced that the earth is a globe but the Chinese were sure it was flat. Yet both invented the equator thousands of years ago. They did so by clocking the lengths of summer and winter days and by observing a belt of sky called the zodiac. This is the celestial highway of the sun, the moon and the major planets. It also includes 12 constellations that parade overhead with the changing seasons.

The zodiac did not fit the neat lines running due north and east. It looped across them at an angle of 23 1/2 degrees. On the two shortest days of the year, its path crossed a certain latitude on its way north or'south. This latitude just had to be the equator, the midway point between the two poles. The celestial equator was drawn on the star charts ages before mariners sailed south of the earth's equator, directly below it. The Chinese placed the equator on their imaginary flat earth more then 4,000 years ago. Around 500 B.C., the Greek genius Pythagoros figured the accurate location of the equator on the round globe.

As mariners sailed farther from home, the ancient star charts pointed out their directions and locations on the globe. In the 1200s, Marco Polo used them to map his route from Europe to China. In the 15th and 16th centuries, Spanish and Portuguese sailors rounded South Africa and beheld the starry heavens south of the equator. The great navigator, Ferdinand Magellan, was also a gifted astronomer. Early in the 1500s, he charted the stars above the Southern Hemisphere. But this was thousands of years after various early astronomers had placed the equator in its proper position.

 

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