Birth horoscopes:
A royal affair.

An important political use of astrology was nativity-forecasts: Birth horosocopes. In a time where the king decided everything, it was necessary to know, how a future king would rule.

Was he smart, a fool, or maybe mentally unstable? Did he drink too much? And probably the most fundamental: How was his luck?

Tycho Brahe produced birth horoscopes for King Frederick 2. (his first patron), and the king's three sons: Christian (the 4 th), Ulrick and Hans. The horoscopes seem to be quite fitting.

Especially the one for Christian the 4th, which is also the most elaborated: 27 pages of calculations and 44 pages of interpretation.

Tycho Brahe did not feel at ease with producing them. He pointed out, how an observational error of 4 minutes would result in an inaccuracy of one whole year. At one time Tycho Brahe's friend, Henrik Below, sent the astrologer 2 independent horoscopes, done for the same person. They were almost completely different. Tycho Brahe explained Below, that the horocopes had been calculated after each their startable. None of the astrologers had used actual observations. And both startables were hopelessly inaccurate.