Although one would have assumed that celestial geometry concerns only such properties as the distance, figure and size of celestial objects, Comte defines these as only one class of phenomena in stellar geometry, namely, static phenomena. He spends considerable time explaining how astronomers can determine these static phenomena, that is, measure our distance from various stellar objects, recognise the figure of these objects, investigate their size and even note the density of their atmosphere. Comte also describes the history of attempts to determine the shape of the Earth, noting that even if there has always been room for making details more precise, this does not mean that the advance of science has been just replacing one error with another.
Comte is clearly more interested in the dynamic phenomena involving movement of celestial objects. He recounts in great detail the history of the discovery of Earth’s movement, both around its axis and around the Sun. What Comte finds philosophically interesting in this discovery is that it has forced us to abandon the theological idea of humans as the centre of the whole universe and also the teleological idea of planets moving for some purpose. This does not mean that astronomy has made the world meaningless, he soothes the reader, since through it we have found the lofty idea of humans as intelligences discovering the laws of the universe even from an insignificant vantage point.
A second important consequence of these discoveries is, Comte says, that we must distinguish the notions of world and universe. By world he means our region of universe, consisting of Earth and its nearby celestial objects – effectively, the Solar System. While people of earlier times could have thought that there is nothing beyond this world, modern astronomy must assume that the universe continues beyond our world, even if we cannot say anything certain about what happens beyond the confines of our world.
It is just to be expected that Comte still has much to say about the three laws of Kepler. He is especially keen to point out that Kepler had to overcome former mythological ideas, involving the notion of a circle as the perfect and thus the only suitable orbit for the supposedly divine stars. The great effect of these laws, Comte suggests, is that they allow us to make predictions about the orbits of planets, satellites and comets. Yet, he adds, even these laws are mere approximations of celestial mechanics – the topic of my next post.
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