Global Positioning System Reference
In-Depth Information
Early Celestial Navigators
The navigational knowledge of ancient Europeans from the classical period
also was very limited. Such knowledge as existed had been gleaned over
centuries, and came and went with each passing civilization: sometimes
knowledge was passed on, and sometimes not. Thus, a very early Mediter-
ranean civilization, the mysterious Minoans of Crete, a Bronze Age people
of the third and second millennium BCE, must have known something
about navigating open seas because we know that they sailed from Crete to
Egypt (fig. 5.2), and in those days such a voyage required spending several
nights out of sight of land. The Minoans knew about the Pole Star,
9
and they
used Ursa Major (the Great Bear, containing the Big Dipper) to locate it,
much as schoolchildren and other skywatchers do today. Such rudimentary
knowledge of celestial navigation may have been passed on to the ancient
Greeks, or they may have attained it independently. Ursa Major is men-
tioned in this context in Homer's
Odyssey
. By the third century BCE Ursa
Minor was incorporated into the celestial navigator's toolbox, and by the
first century CE Beta Draconis (the star Rastoban) was also incorporated.
One of the early Greek explorers was Pytheas, whom we are about to
meet. He knew of the Pole Star, and he speculated about the connection
between the phases of our moon and the tides. He is known to have used a
gnomon, a very early reference to the use of a navigational tool. Another
famous Greek mariner was Nearchos, the admiral of Alexander the Great's
fleet in the fourth century BCE. Nearchos sailed from the Indus River into
the Arabian Sea, across to the Persian Gulf, and up as far as Susa, in the
southwest of modern Iran. Eudoxus of Cyzicus, in the second century CE,
explored the Arabian Sea from Ptolemaic Egypt, making use of early nauti-
cal charts and maps (and no doubt contributing to later ones) that were
constructed using stereographic or orthographic projections, thanks to the
work of the Greek philosophers we met earlier. Much of this mathematical
knowledge would subsequently be lost for over a thousand years.
Pytheas lived in the fourth century BCE in Massilia, the modern Mar-
seilles, on the south coast of France. The city was founded by the ancient
Greeks, who spread westward along the northern Mediterranean coast just
as their great trading rivals, the Carthaginians, had earlier spread west-
ward along the southern coast. Pytheas is known to us because of an
9. In the time of the Minoans, the Pole Star was not Polaris but Draco.
