Augustus and Capricorn: Astrological Polyvalency and Imperial Rhetoric

Abstract

At the beginning of the seventeenth century the great astronomer Kepler wrote to his patron, the Habsburg emperor Rudolf II:Most noble lord, I have now for several weeks on end devoted my utmost efforts to the nativity of Caesar Augustus, about which your kingly majesty wishes to know, but, as I see, it has been almost in vain. For although it is no specially difficult task to calculate the configuration of the heavens for a particular time, nevertheless, what is lacking in the nativity we are now considering is that we no longer today know the correct time of it.The unfortunate astronomer had spent considerable time combing the evidence of the ancient authors available to him about the date of Augustus' birth. He attempted to sift through the conflicting evidence about which day would have been Augustus' birthday, before performing complex calculations of the planetary movements, in order to assess the role Capricorn might have played in his horoscope. His ingenious solution to the problem failed to impress Rudolf, as we can see from Kepler's second letter on the subject (the emperor's letters are not extant):Most noble lord, your kingly majesty has suspected me of a lack of diligence, as though I had not sufficiently reported the nativity of Augustus…