(fl. Athens, fifth century b. c.)
Euctemon is cited (with Meton) by Ptolemy for observations of the summer solstice, including that of 27 June 432 b.c., the reliability of which was doubted by both Ptolemy (Almagest, III, 1) and Hipparchus (modern calculations show that the solstice actually occurred about a day and a half later) but which was still used, as the earliest observation available, to confirm the final Hipparchian Ptolemaic figure of 365.25 less 1/300 of a day for the length of the solar year. Euctemon collaborated with Meton in suggesting a regular intercalation cycle of nineteen years (the Metonic cycle) to correlate the lunar month with the solar year (see B. L. Van der Waerden, in Journal of Hellenic Studies, 80 ,170); this cycle contained 235 lunar months (seven of which were intercalary) and 6,940 days, giving a mean lunar month about two minutes too long and a solar year of 365 5/19 days (some thirty minutes too long). According to Geminus (Iagoge, VIII, 50), who connects Euctemon but not Meton with this cycle (Meton’s name may have dropped out of the text; see Manitius, ad loc.), 110 of the months were “hollow” (i.e., twenty-nine days each) and 125 “full” (thirty days).
Euctemon is frequently cited—some forty-five times in the calendar attached to Geminus’ Isagoge (Manitius, ed., pp. 210 ff.), over fifty times in Ptolemy’s Phaseis, and often in the other Greek calendars (published in Sitzungsberichte der Heidelberger Akademie der Wissenschaften, phil.-hist. Klasse, 1 ; 2 ; 3A , which contains a conjectural restoration by Rehm of Euctemon’s “parapegma”; 4 ; and 5 )—for “weather prognostications” (ἐπισημαίαι)such as formed part of a parapegma, which was a type of almanac, originally engraved on stone or wood, and later transmitted in manuscript form, giving astronomical and meteorological phenomena for the days of each month. His and Meton’s parapegma may well have been the first influential text of this kind in Greece (see A. Rehm, “Parapegmastudien,” in Abhandlungen der Bayerischen Akademie der Wissenschaften, phil.-hist. Abt., n.s. 19 ).
Euctemon is the earliest name mentioned in connection with equinoxes in the extant parapegmata and, according to a second-century b.c. papyrus known as the Ars Eudoxi (F. Blass, ed. [Kiel, 1887]—perhaps a student’s exercise, containing many errors, partly based on Eudoxus’ work with later material added), he gave the lengths of the astronomical seasons, starting from the summer solstice, as ninety, ninety, ninety-two, and ninety-three days, respectively. This shows that he was aware of the nonuniformity of the sun’s course round the earth, but it is unlikely that his parapegma was arranged according to zodiacal months, as later ones were. Ptolemy says (Phaseis, in Claudii Ptolemaei opera quae extant omnia, J. L. Heiberg, ed., II [Leipzig, 1907], 67) that Euctemon made observations at Athens, in the Cyclades, and in Macedonia and Thrace. Rehm thinks that the pseudo-Theophrastian treatise De signis (Theophrasti Eresii opera quae supersunt omnia, F. Wimmer, ed., III [Leipzig, 1862], fr. 6, pp. 115–130) conceals an original meteorological work by Euctemon, but this is pure conjecture.
Euctemon also did some work in geography and is cited by Avienus (fourth century a.d., but using much older sources) for information concerning the straits of Gibraltar (Ora maritima, 337, 350 ff.). Avienus calls him both an Athenian (47–48, 350) and an inhabitant of Amphipolis (337), and he may have been among the Athenian colonists who established a new foundation there in 437 b.c.
In addition to the works cited in the text, see A. Rehm, “Euktemon 10,” in Pauly-Wissowa, XI (1907), cols. 1060–1061.
D. R. Dicks