Ibn Yunus művéről:

 

"Ibn Yunus's major work, an astronomical handbook, was al-Zij al-Hakimi al-kabir. 'Al-kabir' means 'large' which is apt and 'al-Hakimi' means that the work is dedicated to Caliph al-Hakim who certainly supported ibn Yunus. The book is certainly large, containing 81 chapters. There are lists of observations made by Yunus and also observations made by his predecessors. In fact it is a rather remarkable fact that singles the work out from all similar works of that period. Other authors never distinguished between their observations and those in their works which had been made by other scientists.

 

He describes 40 planetary conjunctions accurately and 30 lunar eclipses which were used by Simon Newcomb in his lunar theory. To give an example of a planetary conjunction described in the Hakimi Zij we quote from [2] (see also [1]) having changed the dates given by ibn Yunus to those of a modern calendar:-

 

A conjunction of Venus and Mercury in Gemini, observed in the western sky: The two planets were in conjunction after sunset on the night [of Sunday 19 May 1000]. The time was approximately eight equinoctial hours after midday on Sunday ... . Mercury was north of Venus and their latitude difference was a third of a degree.

 

We can confirm, using modern knowledge of the positions of the planets, that ibn Yunus was exactly right in his description and that the distance of one third of a degree that he gives is again exactly right. He also describes an eclipse of the moon [2]:-

 

This lunar eclipse was [on 22 April 981]. We gathered to observe this eclipse at al-Qarafa, in the Mosque of Ibn Nasr al Maghribi. We perceived first contact when the altitude of the moon was approximately 21. About a quarter of the lunar diameter was eclipsed, and reemergence occurred about a quarter of an hour before sunrise.

 

The first chapter of the Hakimi Zij gives calendar tables for Muslim, Coptic, Syrian and Persian calendars. Ibn Yunus gives tables to convert dates between these calendars. Tables to compute the date of Easter are also given. Trigonometric functions are given as arcs rather than angles. Spherical trigonometry reaches a high level of sophistication in this work."

 

 

 

No nézzük:

 Csillagászati visszaszámolással a normális kronológia szerinti 1000. május 19-én este 8-kor a Vénusz és a Merkur valóban együttálltak, ahogy Ibn Yunus írja, rektaszcenzióban 1 perc, deklinációban kevesebb mint 1/3 fok a különbség. És éppen az Ikrekben (Gemini) vannak.

 

Mi a helyzet 190 év múlva?

 

Ugyanígy állnak?

 

Igen vagy nem?

 

A vasárnapot most nem is firtatom :))