This instrument of very high complexity in its geometric design and of remarkable sharp engraving reached an angular accuracy around one degree.
Muslim astronomers have developed this instrument for centuries, from the late second century AH. Nearly all celestial phenomena were used as references or studied: solstices, equinoxes, eclipses, planet motions. The precision was so high that the error brought by the precession of the equinoxes can now be used to date the instrument.
In seeking the knowledge of the sky, astronomers also aimed at astrology and watched the zodiacal signs.
The Sultan Bayezid II encouraged astronomy. Two astrolabes made for the use of his court are known. One of them is estimated £ 800K, for sale by Sotheby's in London on October 8, lot 135.
This brass instrument of 9.5 cm diameter is complete with all its fixed and rotating parts. The knob for the rotation on the central axis is later.
This astrolabe is indeed a masterpiece of Ottoman science, with numerous engraved inscriptions and reduced decoration. The choice of the reference star is made by the user among no less than fifteen star pointers.
It is signed and dated 911 AH, corresponding to 1505 to 1506 in our calendar. The fact that the author is not otherwise recorded just means that he did not write a treatise.