Rene-NASA-Mooned-America

Space Navigation / Chap. 7 p. 57
SPACE NAVIGATION
When man first journeyed out onto water, he navigated in the same manner that he used
on land: he saw where he wanted to go and pushed himself in that direction. It was an aiming
process. To this day, whenever there is good visibility and deep water in a harbor or river,
this is still the method used. It is called piloting or the taking of visual bearings. Over the
years many piloting aids have been developed such as the compass, depth finders, charts,
buoys, and lighthouses. With these instruments the pilot determines his present location and
aims the boat to the desired location, whether it be a fishing hole out of sight of land or a
dock across a broad bay.
Centuries passed and boats became safer, enabling man to venture further from shore.
But even with good visibility, once out of sight of land, every wave looks alike. Even when
men tried to steer a straight course a ship would wander, pushed off course by wind and
ocean current. Man slowly developed crude celestial navigation using the observed east to
west motions of the Sun, Moon, and stars, all of which were only usable under conditions of
good visibility.
Whether on land, on sea or in the air, the only way you get to your destination, if it can't
be seen, is by knowing both your approximate current position and the location of your
destination. Once this information is known, in decent weather, it becomes a simple matter
of pointing yourself in the proper direction and going there.
At sea, out of sight of land, there are two ways to do this. The ancient Polynesians used
the stars with the knowledge that night after night they parade over the Earth in almost
exactly the same great circles. The deviation from this course varies only slightly night to
night during the entire year, and the pattern repeats year after year.
The Polynesians learned which stars culminated (reached the zenith) directly overhead a
given island. Since a star will do the same thing for hundreds or thousands of years, that
star becomes a beacon for the world's tallest lighthouse whose footings are located in one
particular geographic location. By sailing to the west of that rising star they could zero in on
their destination without compass or sextant. In this manner, island by island, they learned to
navigate the immense Pacific while European seaman hardly dared leave sight of the coasts.
Asiatic seamen learned similar astral navigation as there is evidence that the Chinese
reached the West Coast of both North and South America. Eventually western astronomers
developed astronomical charts of the Sun that showed its latitude on each particular day.
Since the Sun changes latitude at less than a quarter of a degree per day, if you measure the
altitude of the Sun at high noon you can use this information to create a chart or later to find
your latitude. It involves no more than subtracting the Sun's angle of elevation at high noon
(culmination) from 90° then adding it to the Sun's known latitude that day. Before we get to
navigation in space, it's helpful to know a little more about earthly navigation.
The angle of elevation was first measured by knotted strings held in the hands. The cross
staff evolved into the octant, and eventually became the sextant that is still in use. The bands
of latitude are natural divisions and are determined by the equator and poles. Longi-
NASA MOONED AMERICA! / Rene