The Observant Astronomer

The passing scene as observed by an observant Jew, who daylights as an astronomer.

Wednesday, March 30, 2005

The Great Divide: Objectives

Underlying many of the Torah vs. Science arguments is a mistaken assumption about what the Pre-SR science is doing. Since it is this Pre-SR viewpoint that is taken as the "Torah's" view on the subject, it is worthwhile to try and understand just what the Pre-SR thinkers were doing, and how this differs from Post-SR. Here I will discuss the objectives of the Pre-SR astronomers. Since we are discussing astronomy, we are safe in following the Rambam and making reference to Ptolomaic and Aristotelian concepts.

The first thing to recognize is that the Pre-SR astronomers were essentially working in two dimensions. Their primary concern was to be able to predict the positions of the planets* on the sky. Why? Because these predictions were needed to compute horoscopes.

Call a modern-day astronomer an astrologer and you'll get either a grimace or an ear-full. But for most of our scientific antecedants, right through the Copernican/Keplerian reveloution, the whole point of calculating planetary motions was to be able to know where the planets were at the time for which you need a horoscope. So the entire objective was to calculate where the seven planets were with respect to the fixed stars. Kepler's Rudolphine Tables were such a hit because they did this with a much greater accuracy than any previous set of tables.

Of secondary concern was the third dimension, i.e. the distances of the planets. It was well understood that these are not constant, since the "sizes" of the planets changes. By "size" what they meant was "brighness", since, with the exception of the Sun and Moon, planetary disks are effectively unresolved by the human eye. But solar eclipses, when the Moon passes in front of the Sun, provided clear evidence that the relative sizes of the Sun and Moon changed, because sometimes, even when the Moon passes across the center of the Sun's disk, a ring of light is left behind, forming an annular rather than a total eclipse.

In any event, the best they could do was to give relative rather than absolute distances for the planets, usually by nesting the spheres that contained the circles on which the planets travelled, but, even then, the resulting size variations were often not in accord with reality. This didn't bother them overmuch, since the angular positions on the sky were coming outacceptably, but it poses a big problem if you are planning on sending a physical object to one of those planets.

* In Pre-SR astronomy the planets, in order of distance from the Earth are: Moon, Mercury, Venus, Sun, Mars, Jupiter, Saturn. In some schemes Mercury and Venus were switched. These were the objects that wandered in the heavens


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