Incidental to talking about the celestial spheres [III, 14], the Rambam mentions some facts about astronomy as the Sages related them. For example, he mentions that the distance from Saturn to Earth is a journey of approximately 8,700 solar years. The Rambam suggests that a day’s travel is about 40 mil of 2,000 cubits each, which would be in the vicinity of 25 miles.
We, however, know that Saturn is 746 million miles from the Earth. 8,700 years would be 3,177,675 days. To cover this distance in the time specified, one would need to travel almost 235 miles a day. This is far more than one could travel per day even by horse. (Presumably the Sages were not talking about how far one could travel by ship and even that number falls short by quite a bit.)
Should we be bothered that the Rambam’s science, based upon teachings of the Sages, is so far off-base from what we know to be correct? Not at all. The Rambam notes that even in his day, those familiar with astronomy said that his numbers were not accurate. It’s interesting to note that the astronomers of the Rambam’s day said that the Sages’ distances were far too big, while they’re actually too small according to our science. In any event, the Rambam isn’t concerned.
We can’t expect everything the Sages said about astronomy to concur with our own observations, he says, because math and science were not as advanced in Talmudic times as they would become in the Rambam’s day, let alone our own. Their statements about scientific matters were not traditions received from the prophets, they were simply the best facts available to science at the time.
When the Sages’ science is off, the Rambam does not hesitate to acknowledge that reality. When they are correct, he does not minimize it by suggesting that they “got lucky” every once in a while. Just the opposite, the Rambam tells us that whenever the Sages’ words can be understood in a manner consistent with the established facts, it is appropriate for us to do so.