[QUOTE=CalMeacham]
Incidentally, I believe the question anbout the association of Jupiter with the large gas giant has come up on this Board before, quite a long time ago. It seems at first glancde appropriate that the largest of these “Wanderers” (which is what “planet” means) should be associated with the King of the Gods – but there’s no way that the Greeks and Romans would have known that Jupiter was the largest. They had no telescopes, and Venus is brighter than Jupiter. Saturn is farther out, and has a longer orbit. Why Jupiter was associated with the Head God isn’t clear to me.
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Per the Greek cosmology, the planets, Sun, and Moon all orbited the Earth in the following order: Saturn, Jupiter, Mars, Sun, Venus, Mercury, and the Moon (Sun and Moon were considered planets, not–as they are today–separate cosmic phenomena). The Greeks deduced this order under the general principle that the length of time it took a planet to return to the same point in the sky was proportional to its distance from Earth. For the inferior planets (which the Greeks noted never strayed too far from the Sun), this was understood to be the planet’s position relative to the Sun, so they naturally assumed, since Mercury was faster than Venus, it was closer to Earth.
According to Pliny (II.8), this view was supported by the observation that Venus was the brightest of the planets (because it was so near the Sun) and that Mars was the hottest (because of its bright red color). Saturn was the furthest planet from the sun, and so was the coldest. “And so it is, that by the exceeding heat of Mars and the terrible cold of Saturn, Jupiter, who is placed betwixt, is well tempered of them both, and so becomes good and comfortable.”
This notion of balance between extremes may seem quaint to us today, but it is a foundational tenet of classical civilization; Zeus/Jove was more than just the most powerful of the gods, he was considered a judge and moderating force among the divinities.
One final note. It’s been pointed out that the “wandering” of the planets in the night sky was a reason to think of them as divine. This is true, but one should also note that the planets regularly change in magnitude, which would make a Greek observer believe the planet is moving closer to or farther away from the Earth or Sun. This, in fact, was one of the reasons Ptolemy’s epicycle theory (wrong as it is) was so appealing; it didn’t just explain retrograde motion, but also explained why the planets varied in magnitude. Like many ancient theories, the details weren’t pressed too hard, and obviously no further progress could be made until the whole notion of an Earth-centric system was abandoned.
I state this only because, as commonplace as the notions of planetary orbit are to us today, we sometimes fail to realize they are the result of more detailed investigation and appear at first glance counter-intuitive. The ancients weren’t stupid, or slavish in preserving certain cosmological beliefs, they simply arrived at different conclusions based on their own observations–ones that seemed reasonable given their limited knowledge–and didn’t think to scrutinize beyond common sense.