Editing Pytheas (section)

=== 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 [[Ionia]]n 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 model<ref>''Geographica'' [https://penelope.uchicago.edu/Thayer/E/Roman/Texts/Strabo/2E1*.html II.5.3].</ref> 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, [[Tropic of cancer|Cancer]] and [[Tropic of Capricorn|Capricorn]]. During noon of the [[summer solstice]] (therinē tropē) rods there cast no shadow.<ref>''Geographica'' [https://penelope.uchicago.edu/Thayer/E/Roman/Texts/Strabo/2E1*.html II.5.7].</ref> 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.<ref>Strabo's extensive presentation of the geographic model including the theory of the Arctic is to be found in [https://penelope.uchicago.edu/Thayer/E/Roman/Texts/Strabo/2E1*.html Book II Chapter 5].</ref>

Seen from the equator the celestial North Pole (''boreios polos'') is a point on the horizon. As the observer moves northward the pole rises and the [[circumpolar stars]] appear, now unblocked by the Earth. At the Tropic of Cancer the radius of the circumpolar stars reaches 24°. The edge stands on the horizon. The [[constellation]] of ''mikra arktos'' ([[Ursa Minor]], "little bear") was entirely contained within the circumpolar region. The latitude was therefore called the ''arktikos kuklos'', "circle of the bear". The terrestrial Arctic Circle was regarded as fixed at this latitude. The celestial Arctic Circle was regarded as identical to the circumference of the circumpolar stars and therefore a variable.

When the observer is on the terrestrial Arctic Circle and the radius of the circumpolar stars is 66° the celestial Arctic Circle is identical to the celestial [[Tropic of Cancer]].<ref>{{harvnb|Nansen|1911|p=53}}.</ref> That is what Pytheas means when he says that Thule is located at the place where the Arctic Circle is identical to the [[Tropic of Cancer]].<ref name=straboII-5-8 /> At that point, on the day of the [[Summer Solstice]], the vertical rod of the [[Gnomon|gnōmōn]] casts a shadow extending in theory to the horizon over 360° as the Sun does not set. Under the pole the Arctic Circle is identical to the Equator and the Sun never sets but rises and falls on the horizon. The shadow of the gnōmōn winds perpetually around it.