1 The Birth of Science - MSRI

272 10. Lost Science
Apollonius Myndius thinks otherwise. He says that a comet is not
made up of many planets, but rather that many comets are planets.
He says: “A comet is not a false appearance nor an extension of fire in
the neighborhood of two stars, but a heavenly body in its own right,
like the sun and the moon. Its shape is just like that, not enclosed in a
circle but more elongated and stretched out. Moreover it has an orbit
that is not openly visible; it crosses the upper regions of the universe
and appears only when it reaches the lowest point of its orbit. 148
The statement about the “shape” probably referred to the orbit in the
source, though Seneca may not be aware of it. For even admitting that
an astronomical source would linger and say that the tail of a comet is
“more elongated” than a circle, we would lose the clear logical connection
with the next sentence, which evidently implies in any case that the orbit
is elongated. page 339
The notion that comets are celestial bodies of the same type as planets,
which Seneca attributes to Apollonius of Myndius, is mentioned also by
Aetius, who attributes them to some Pythagoreans, 149 and to Pliny, who,
without attributing the opinion to anyone in particular, says of the comets:
“Some move like planets, others remain fixed.” 150 It may be suspected
that the immobility option (which is contrary to all observable facts) was
added by Pliny, to whom the notion that all comets without exception
shared the planets’ vagrancy may have seemed too far-fetched. But the
association between comets and planets must have been a widespread
idea in pre-Ptolemaic times, because, other than in Pliny, Seneca and the
Pythagoreans mentioned by Aetius, it can be found also in Manilius. This
character, who wrote an astrological poem some time in Augustus’ and
Tiberius’ reign, mentions three different theories about comets; according
to one (the most interesting for our purposes), the sun periodically attracts
the comets to itself and then lets them go, as it does with Mercury and
Venus. 151
148 “Apollonius Myndius in diversa opinione est. Ait enim cometen non unum ex multis erraticis
effici, sed multos cometas erraticos esse. Non est, inquit, species falsa nec duarum stellarum confinio
ignis extentus, sed proprium sidus cometae est, sicut solis ac lunae. Talis illi forma est, non in
rotundum restricta sed procerior et in longum producta. Ceterum non est illi palam cursus; altiora
mundi secat et tunc demum apparet cum in imum cursus sui venit.” (Seneca, Naturales quaestiones,
VII, xvii, 1–2).
149 [DG], 366.
150 “Moventur autem aliae errantium modo, aliae immobiles haerent” (Naturalis Historia, II, 91).
151 Manilius, Astronomica, I, 867–875.
Revision: 1.11 Date: 2003/01/06 02:20:46