Regiomontanus and Placidean under the pole directions

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 Giuseppe Bezza, unpublished )) .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?

Continue reading Regiomontanus and Placidean under the pole directions

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