In the latest post (( http://heavenastrolabe.net/semiarc-and-alchabitius-directions/ )) we saw as semiarc (or alchabitius, which is another way to collect numbers) fits very well with Ptolemy’s example given in Tetrabiblos III, 10 (( Ptolemy. Tetrabiblos. Translation Frank Robbins. Cambridge Mass. ;London: Harvard University Press ; W. Heinemann, 1980. I’ve used the Italian translation cura Prof. Giuseppe Bezza, unpublished )) . But what about Regiomontanus and “under the pole” directions? Are they different methods? Are they congruent to Ptolemy?
Since the Antiquity astrology (and prediction) was based on astronomical tables generally divided into three different parts collected together: tables of primum mobile, tables of planetary positions, eclipses; at the beginning of the Renaissance tables of primum mobile were separated from the rest: the most famous of all Regiomontanus’ ones, which the author called “Tables of directions” because they were used in order to calculate directions. (( Johannes Regiomontanus, Tabulae directionum profectionumque, non tam Astrologiae iudiciariae, quam tabulis instrumentisque innumeris fabricandis utiles ac necessariae, several editions ))