Leonid Zhmud The Origin of the History of Science in Classical Antiquity

archus, 132f.; von Fritz. Oinopides, 2262f.; Bulmer-Thomas, I. Oinopides of Chios,
DSB 10 (1980) 179f.

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5. Oenopides of Chios
265
measuring the obliquity of the ecliptic. The ecliptical motion of the planets (in-
cluding the sun and the moon) was known to the early Pythagoreans (24A 4).
160
Once the concept of the ecliptic is introduced, the inclination of the ecliptic
with respect to the celestial equator immediately follows from it. Oenopides’
discovery consisted most probably in the measurement of the angle between
them, and not in establishing the very fact of inclination.
161
But since Dercyl-
lides-Theon removes Oenopides’ name from its context and places it before
Thales, this discovery appeared to be divided into two parts, the first of which,
“discovered the obliquity of the zodiac”, was attributed to Oenopides, while the
second, “that the axis of the fixed stars and that of the planets are separated
from another by the side of a (regular) pentadecagon”, was attributed to the
anonymous oî loipoí (fr. 145).
The fact that the empirically found angle of the obliquity of the ecliptic was
expressed via the side of the pentadecagon inscribed in a circle betrays the Py-
thagorean influence, as was rightly pointed out.
162
The regular fifteen-angled
figure inscribed in a circle does, indeed, conclude book IV of the
Elements
(which belongs to the Pythagoreans);
163
it consists of a regular pentagon (from
which the dodecahedron attributed to Hippasus was constructed) and an equi-
lateral triangle, whose properties also attracted Pythagorean attention.
164
It is,
in fact, only one of many traces that reveal that Oenopides’ mathematical as-
tronomy was largely indebted to the mathematics and astronomy of the early
Pythagorean school. The Pythagoreans themselves may well have moved in the
same direction at the same time as Oenopides: the unification of the four
ma-
the¯mata into a group of ‘related’ sciences, accomplished by the mid-fifth cen-
tury at the latest,
165
would not have taken place had not the Pythagorean astron-
omy already acquired features manifestly akin to geometry.
The sources attribute to Pythagoras himself the discovery of the earth’s
spherical shape, the identification of the Morning and the Evening star with
Venus, and the division of the celestial sphere into zones.
166
His priority in the
first two discoveries is contested by Parmenides, whose name is also associated
with the division of the earthly sphere into zones.
167
Without entering into the
160
The other contenders for this discovery are 1) Anaximander (12 A 5, 22); see Guth-
rie,
op. cit., 96f.; cf. Couprie, D. The visualization of Anaximander’s astronomy,
Apeiron 28 (1995) 159–182; 2) Cleostratus (6 B 2); 3) Anaxagoras (59 A 1.9); see
Dicks.
Early Greek astronomy, 59.
161
Von Fritz. Oinopides, 2260f.; Burkert.
L & S, 306 n. 38; Gundel. Zodiakos, 490; van
der Waerden.
Pythagoreer, 349; Szabó, Maula, op. cit., 120f.
162
Heath.
Aristarchus, 131 n. 4; von Fritz. Oinopides, 2261; Neugebauer. HAMA II,
629.
163
See above 171 n. 22.
164
See above, 170, 198.
165
See above, 63f.
166
Aët. II,12.1, III,14.1; Aristox. fr. 24; D. L. VIII, 48.
167
28 A 4, 44a; D. L. IX, 23, cf. 28 A 40a.

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Chapter 7: The history of astronomy
266
debate on priorities,
168
let us highlight the main point: the tradition relates all
these discoveries to the threshold of the fifth century. By that time, the Pytha-
goreans already knew that the planets move in a direction opposite to that of the
fixed stars.
169
The discovery of the earth’s spherical shape led to the formation
of the main astronomical model of antiquity, which consisted of two concentric
spheres, the stellar and the terrestrial one.
170
The division of the celestial sphere
into zones implies some notion of the celestial equator and two tropic circles
crossed by the oblique circle of the zodiac. Even if the early Pythagoreans and
Parmenides did not fully elaborate these geometrical notions, they are present
as such in Hippocrates: the terrestrial sphere is inside of the celestial one, both
of them are divided into zones; the planets move in circular orbits along the
ecliptic, and the horizon divides these orbits into unequal segments.
171
This
means that Oenopides, an older contemporary and likely a teacher of Hippo-
crates, was directly involved in the elaboration and dissemination of geometri-
cal astronomy and of the ‘double-sphere’ model of the cosmos.
The passage in Dercyllides–Theon that starts (a, b) and ends (e) with Oeno-
pides’ discoveries helps us to define more precisely the scope of the problems
he worked on:
Oenopides was the first to discover (a) the obliquity of the zodiac and (b) the peri-
od of the Great Year … (he is followed by Thales, Anaximander, Anaxagoras).
And others discovered in addition to this that (c) the fixed stars move round the
immobile axis that passes through the poles, (d) whereas the planets move round
the axis perpendicular to the zodiac; and that (e) the axis of the fixed stars and that
of the planets are separated from one another by the side of a (regular) pentade-
cagon (fr. 145).
172
168
See Zhmud.