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Kitab al bulhan or "book of surprises" is medieval Persian manuscript written in Arabic.

According to Wikipedia:

The contents include subjects on astronomy, astrology and geomancy, including a section of full-page illustrations, with plates dedicated to the discourse topic, e.g. a folktale, a sign of the zodiac, a prophet, etc.

It has following illustration in one of its pages (archive.org page 243). It is the only drawing in the book that has geometrical figures in it. (edit: i was wrong - there are actually many tables and diagrams)

Do you have any idea what it is about and is it related to astronomy? Is it some kind of calendar?

enter image description here

Google text translation works some of the words:

enter image description here

So it looks like there are "north" and "south" and some names of star constellations, stars etc. Maybe zodiac stars/constellations? It may be related to astronomy or astrology.

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    $\begingroup$ Any context? Can you translate any of the writing? $\endgroup$
    – ProfRob
    Commented Jan 16, 2023 at 12:23
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    $\begingroup$ i found this article about the book slv.vic.gov.au/sites/default/files/… . according to wikipedia "The contents include subjects on astronomy, astrology and geomancy, including a section of full-page illustrations, with plates dedicated to the discourse topic, e.g. a folktale, a sign of the zodiac, a prophet, etc. " en.wikipedia.org/wiki/Book_of_Wonders. I dont know is this drawing related to astronomy or something else. This looks like to be only drawing in the book that looks to have geometric figures. I can't translate it. $\endgroup$
    – SamiM
    Commented Jan 16, 2023 at 13:58
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    $\begingroup$ looks like all or most of the drawings of kitab al bulhan can be found in wikimedia commons site: commons.wikimedia.org/w/… $\endgroup$
    – SamiM
    Commented Jan 16, 2023 at 14:09
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    $\begingroup$ Perhaps a better subject for History or History of Science and Mathematics. $\endgroup$ Commented Jan 16, 2023 at 14:35
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    $\begingroup$ Aye, the translation somewhat hints that it is about astronomy. I retracted my close vote. $\endgroup$ Commented Jan 16, 2023 at 20:23

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The central part of the diagram looks like it's illustrating the obliquity of the ecliptic. My guess is that the main vertical line is the ecliptic and the curve shows the declination of the Sun.

From top to bottom, the ecliptic longitude runs down from 0° to 180° (March equinox, June solstice, September equinox) with the corresponding declination curve on the right / south side, and then back up again from 180° to 360° (September equinox, December solstice, March equinox) on the left side.

Here's an equivalent diagram, using more modern conventions, and the J2000 value for the obliquity (~23.44°).

Declination diagram

Plotting script

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