Editing Pytheas (section)

=== Latitude by length of longest day, and by Sun's elevation on shortest day ===
Strabo used the astronomical cubit (''pēchus'', the length of the forearm from the elbow to the tip of the little finger) as a measure of the elevation of the Sun. The term "cubit" in this context is obscure; it has nothing to do with distance along either a straight line or an arc, does not apply to celestial distances, and has nothing to do with the gnōmōn. [[Hipparchus]] borrowed this term from [[Babylonia]], where it meant 2°. They in turn took it from ancient [[Sumer]] so long ago that if the connection between cubits and degrees was known in either Babylonia or Ionia it did not survive. Strabo stated degrees in either cubits or as a proportion of a [[great circle]]. The Greeks also used the length of day at the summer solstice as a measure of latitude. It is stated in equinoctial hours (''hōrai isēmerinai''), one being 1/12 of the time between sunrise and sunset on an [[equinox]].

Based partly on data taken from Pytheas, Hipparchus correlated cubits of the Sun's elevation at noon on the winter solstice, latitudes in hours of a day on the summer solstice, and distances between latitudes in stadia for some locations.<ref>{{harvnb|Nansen|1911|p=52}}.</ref> Pytheas had proved that Marseille and Byzantium were on the same parallel (see above). Hipparchus, through Strabo,<ref>Strabo [https://penelope.uchicago.edu/Thayer/E/Roman/Texts/Strabo/2A1*.html II.1.12,13].</ref> added that Byzantium and the mouth of the Borysthenes, today's [[Dnieper]], were on the same [[Meridian (geography)|meridian]] and were separated by 3700 stadia, 5.3° at Strabo's 700&nbsp;stadia per a degree of [[meridian arc]]. As the [[Circle of latitude|parallel]] through the river-mouth also crossed the coast of "Celtica", the distance due north from Marseille to Celtica was 3700 stadia, a baseline from which Pytheas seems to have calculated latitude and distance.<ref>However, Srabo [https://penelope.uchicago.edu/Thayer/E/Roman/Texts/Strabo/2A1*.html II.1.18] implied 3800, still attributed to Hipparchus. [[Eratosthenes]] has quite a different view. See under [[Thule]].</ref>

Strabo said that Ierne (written Ἰέρνη, meaning Ireland<ref>[[Éire#Etymology]]</ref>) is under 5000 stadia (7.1°) north of this line. These figures place Celtica around the mouth of the [[Loire]], an emporium for the trading of British tin. The part of Ireland referenced is the vicinity of [[Belfast]]. Pytheas then would either have crossed the [[Bay of Biscay]] from the coast of Spain to the mouth of the Loire, or reached it along the coast, crossed the [[English Channel]] from the vicinity of [[Brest, France]] to [[Cornwall]], and traversed the [[Irish Sea]] to reach the [[Orkney]] Islands. A statement of Eratosthenes attributed by Strabo to Pytheas, that the north of the [[Iberian Peninsula]] was an easier passage to Celtica than across the Ocean,<ref>[https://penelope.uchicago.edu/Thayer/E/Roman/Texts/Strabo/3B*.html Strabo III.2.11].</ref> is somewhat ambiguous: apparently he knew or knew of both routes, but he does not say which he took.

At noon on the [[winter solstice]] the Sun stands at 9 cubits and the longest day on the [[summer solstice]] is 16 hours at the baseline through Celtica.<ref>Strabo II.1.18. The notes of the Loeb Strabo summarized and explained this information.</ref> At 2500&nbsp;stadia, approximately 283 miles, or 3.6°, north of Celtica, are a people Hipparchus called Celtic, but whom Strabo thought were the British, a discrepancy he might not have noted if he had known that the British were also Celtic. The location is Cornwall. The Sun stands at 6&nbsp;cubits and the longest day is 17&nbsp;hours. At 9100&nbsp;stadia, approximately 1032&nbsp;miles, north of Marseille, 5400 or 7.7° north of Celtica, the elevation is 4&nbsp;cubits and the longest day is 18&nbsp;hours. This location is in the vicinity of the [[Firth of Clyde]].

Here Strabo launched another quibble. Hipparchus, relying on Pytheas, according to Strabo, placed this area south of Britain, but he, Strabo, calculated that it was north of Ireland (Ierne/Ἰέρνη). Pytheas, however, rightly knew what is now [[Scotland]] as part of Britain, land of the [[Picts]], even though north of Ireland/Ierne. North of southern Scotland the longest day is 19 hours. Strabo, based on theory alone, states that Ierne is so cold<ref name=straboII-5-8 /> that any lands north of it must be uninhabited. In the hindsight given to moderns Pytheas, in relying on observation in the field, appears more scientific than Strabo, who discounted the findings of others merely because of their strangeness to him. The ultimate cause of his skepticism is simply that he did not believe Scandinavia could exist. This disbelief may also be the cause of alteration of Pytheas' data.