mch

106 OUR ANCESTORS CAME FROM OUTER SPACE
kinds of silly proposals were made how to improve navigation
over wide oceans. None of them was so simple and efficient
as
the ancient moonrise tables. Some scientists proposed to measure
simultaneously the angle between the moon and certain stars
that is different at different points of the globe, but the precision
needed for such measuring makes it impractical for small instruments
aboard a ship. It was even proposed that a satellite of
Jupiter be observed for calculation of longitude at sea, an operation
that I certainly would not Uke to be in charge of, since
Jupiter is above us only in daytime and no pair of binoculars usable
aboard a ship will show its moons.
Another fanciful proposal without any practical merit was to
anchor ships on each meridian and let them shoot colored flares
every hour on the hour to indicate longitude to vessels passing
by. But how do you measure exact distance over open water
with the techniques that were at the disposal of seamen in the
nineteenth century? And how do you anchor a ship in mid-
Pacific? The well-known American writer of the last century Edward
Everett Hale wrote a science-fiction story called "The Brick
Moon," in which he came up with a brilliant idea, and established
himself as the inventor of the navigation satellite, the
backbone of modern navigation today. In Hale's book a manmade
moon constructed of bricks was orbiting our globe with
the precision of a pendulum, probably every ninety minutes. The
time of passage of this satellite through the local meridian gave
the exact longitude much as a passenger on a train that is exactly
on time could tell where the train is just by looking at his watch
and timetable, not out the window.
Today, the navigator of any ship lost in the thickest fog can
easily determine his position within a few hundred feet, an
achievement made possible by the three Transit satellites which
the U. S. Navy in 1961 placed in polar orbits spaced 120 degrees
apart around the equator and circling the earth every ninety
minutes. Every parallel is crossed every thirty minutes, and because
of the rotation of our globe, each following passage is
degrees more in a westerly direction than the preceding one.
After three passages of the satellites overhead, the ship's navigator
can trace a very small triangle on his chart and knows that
he is within these limits. The principle is very simple and only an
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