Comments on: Primary Directions: the story of calculations (vol. 3)

By: Dr. H.

Dr. H. — Wed, 18 Feb 2009 00:49:42 +0000

Thanks for the clarification. Look forward to further entries. Your historical review is very helpful.

- Dr. H.

By: Anton Grigoryev

Anton Grigoryev — Tue, 17 Feb 2009 21:17:17 +0000

Directions of Alcabitius and of Ptolemy are the same in essence, but their mathematical solutions are different. It’s just two ways to calculate the same. You can get Alcabitius’s algorithm from Ptolemeaic, if you disintegrate in formulas temporal hours etc. and then make some transformations of the formulas.
Rumen Kolev is right, we can call it ‘Placidus Classic’, in a way. But first, it is zodiacal directions (i.e. promittor is a point of the ecliptic), not mundane (promittor is the real celestial body). Placidus preferred mundane directions. Secondly, significator in both Ptolemy and Alcabitius is a point of ecliptic, too. Placidus didn’t directed this way. His significator is a real celestial body. Except these two important peculiarities, both Ptolemaic and Alcabitus’s directions are similar to Placidean Classic.

Anton

By: Dr. H.

Dr. H. — Tue, 17 Feb 2009 19:00:07 +0000

So Ptolemy represents a development in primary directions technique which improves on the Hellenistic attempts by using the correct model for the celestial sphere. But it appears to fall short of the Alchabitius method. I ask because Rumen Kolev stated when reviewing Zoller’s algorithm for the Alchabitius method that Zoller’s algorithm was equivalent to what Kolev names ‘Placidus Classic’ or ‘Ptolemy.’ But it sounds like Alchabitius and Ptolemy are two different models, true? Just trying to get the terminology straightened out.

- Dr. H.

By: Anton Grigoryev

Anton Grigoryev — Fri, 06 Feb 2009 14:14:43 +0000

Thanx for your kind words
I plan on proceeding with this subject. The next are medieval primary directions from various Arabian, Hebrew and Latin authors, both mainstream and unorthodox.

Anton

By: Ed Falis

Ed Falis — Wed, 04 Feb 2009 19:52:03 +0000

Nice presentation throughout the three articles.

- Ed

By: Dlynne

Dlynne — Wed, 04 Feb 2009 16:05:18 +0000

Thank you so much for this post. I have been trying to get a handle on primary directions as practiced by Ptolemy ever since I read about them 25 years ago in Jacobson’s book “The Turn of a Lifetime.” This column helps a lot.

By: Anton Grigoryev

Anton Grigoryev — Wed, 04 Feb 2009 15:25:52 +0000

You are welcome

Anton

By: yuzuru

yuzuru — Wed, 04 Feb 2009 15:10:28 +0000

Very interesting and important. Thanks for that