Pytheas : biography

Today the elevation can be obtained easily on ship with a quadrant. Electronic navigational systems have made even this simple measure unnecessary. Longitude was beyond Pytheas and his peers, but it was not of as great a consequence, because ships seldom strayed out of sight of land. East-west distance was a matter of contention to the geographers; they are one of Strabo’s most frequent topics. Because of the gnōmōn north-south distances were accurate often to within a degree.

It is unlikely that any gnōmōn could be read accurately on the pitching deck of a small vessel at night. Pytheas must have made frequent overnight stops to use his gnōmōn and talk to the natives, which would have required interpreters, probably acquired along the way. The few fragments that have survived indicate that this material was a significant part of the periplus, possibly kept as the ship’s log. There is little hint of native hostility; the Celts and the Germans appear to have helped him, which suggests that the expedition was put forward as purely scientific. In any case all voyages required stops for food, water and repairs; the treatment of voyagers fell under the special "guest" ethic for visitors.

Location of the Arctic Circle

The ancient Greek view of the heavenly bodies on which their navigation was based was imported from Babylonia by the Ionian Greeks, who used it to become a seafaring nation of merchants and colonists during the Archaic period in Greece. Massalia was an Ionian colony. The first Ionian philosopher, Thales, was known for his ability to measure the distance of a ship at sea from a cliff by the very method Pytheas used to determine the latitude of Massalia, the trigonometric ratios.

The astronomic model on which ancient Greek navigation was based, which is still in place today, was already extant in the time of Pytheas, the concept of the degrees only being missing. The modelGeographica . divided the universe into a celestial and an earthly sphere pierced by the same poles. Each of the spheres were divided into zones (zonai) by circles (kukloi) in planes at right angles to the poles. The zones of the celestial sphere repeated on a larger scale those of the terrestrial sphere.

The basis for division into zones was the two distinct paths of the heavenly bodies: that of the stars and that of the sun and moon. Astronomers know today that the Earth revolving around the sun is tilted on its axis, bringing each hemisphere now closer to the sun, now further away. The Greeks had the opposite model, that the stars and the sun rotated around the earth. The stars moved in fixed circles around the poles. The sun moved at an oblique angle to the circles, which obliquity brought it now to the north, now to the south. The circle of the sun was the ecliptic. It was the center of a band called the zodiac on which various constellations were located.

The shadow cast by a vertical rod at noon was the basis for defining zonation. The intersection of the northernmost or southernmost points of the ecliptic defined the axial circles passing through those points as the two tropics (tropikoi kukloi, "circles at the turning points") later named for the zodiacal constellations found there, Cancer and Capricorn. During noon of the summer solstice (therinē tropē) rods there cast no shadow.Geographica . The latitudes between the tropics were called the torrid zone (diakekaumenē, "burned up").

Based on their experience of the Torrid Zone south of Egypt and Libya, the Greek geographers judged it uninhabitable. Symmetry requires that there be an uninhabitable Frigid Zone (katepsugmenē, "frozen") to the north and reports from there since the time of Homer seemed to confirm it. The edge of the Frigid Zone ought to be as far south from the North Pole in latitude as the Summer Tropic is from the Equator. Strabo gives it as 24°, which may be based on a previous tangent of Pytheas, but he does not say. The Arctic Circle would then be at 66°, accurate to within a degree.Strabo’s extensive presentation of the geographic model including the theory of the Arctic is to be found in .