The Fault Is Not in Our Stars 63have known. Three times in the previous week or so I had read in dif-
ferent horoscopes that my finances were about to take a turn for the
better.’ Even the historians Mann and Diwald were half-inclined to
believe in Kepler’s horoscope for Wallenstein. ‘Were I to say that there
were something to the art of astrology, provided that the right man
does it, I would no doubt provoke a smile on the part of many a reader.
I would happily tolerate that if only I were offered a better explanation.’
Thus wrote Mann. According to Diwald, ‘almost everything which
Kepler predicted was fulfilled’, things which ‘decades later became
reality, mysteriously accurate and almost letter-for-letter true’ – a state-
ment which is manifestly incorrect, as can be seen from the foregoing
analysis of Kepler’s actual texts.^24
By seventeenth-century standards astrology was rational and scien-
tific. Casting a horoscope required advanced mathematical knowledge
and laborious calculations in order to project the positions of the
planets back to the subject’s time and place of birth, and forward to
the times for which predictions were to be made. Interpretation there-
after was not a matter of whim or intuition, but of following the rules
and precedents in the vast body of literature on the subject which had
been built up over the centuries. Two skilled practitioners should in
theory have reached very similar conclusions, although of course not
all were equally competent or diligent while some were charlatans.
The level of acceptance of astrology among the upper classes of the
time can be assessed from the large number of horoscopes prepared
by Kepler which have survived, reportedly thousands, although these
were not necessarily all paid commissions, and he was only one of
many such sages. Moreover astrology had long been embraced by the
establishment, with both the papacy and the Empire maintaining
official astrologers, although the Catholic church had begun to turn
against it after the Reformation. As a result astrology was among the
many subjects covered by the rules on prohibited books issued by the
pope in 1564, with specific reference to works ‘determining destiny by
astrology’ or attempting ‘to affirm something as certain to take place’,
but many practising Catholics nevertheless maintained their interest.
Kepler, a Protestant, wrote to Wallenstein that ‘philosophy, and hence
also true astrology, is a witness to God’s works, and therefore a holy
not a frivolous thing’, implicit in which is the view that the planets
and other heavenly bodies, as God’s creations, were capable of reveal-
ing as much of the truth as God willed.^25 That this in the end turned
out to be a false premise has a parallel in the main astronomical theory
of the day, the Ptolemaic view that the earth was the centre of the