SUG: document new definition of extent

Author: gzotti

guide/ch_skycultures.tex

@@ -469,7 +469,7 @@ \subsection{Constellations}
                     each pair being right ascension $\alpha$ (decimal hours) and declination $\delta$ (decimal degrees) in equinox J2000.0. 
                     See below how Stellarium can help you write these arrays.
 
-                    \indexterm[constellations!single-star]{Single-star constellations}\newFeature{25.1}  or particular highlights can be described with just one star repeated in a two-element segment.
+                    \indexterm[constellation!single-star]{Single-star constellations}\newFeature{25.1}  or particular highlights can be described with just one star repeated in a two-element segment.
                     The respective star will be encircled with a radius of 
 \item[\jtag{single\_star\_radius}] (float, default 0.5)\newFeature{25.1}.
 \item[\jtag{hull\_extension}] (optional)\newFeature{25.2} A vector of star IDs (HIP number as integer, Gaia DR3 long integer number as string, 
@@ -526,7 +526,7 @@ \subsection{Constellations}
 \end{description}
 
 
-\paragraph{Drawing dark constellations}\index{constellations!dark}\label{SC:constellations:dark:markers}
+\paragraph{Drawing dark constellations}\index{constellation!dark}\label{SC:constellations:dark:markers}
 The outlines \newFeature{25.2}of figures like the ``Emu in the Sky'' cannot be described with connect-the-dot star patterns, 
 as they are formed from the absence of luminous patterns. We need to describe them using coordinate lists. 
 To make the process less tedious, we can extend setting Markers (see \ref{sec:tour:markers}). 
@@ -765,6 +765,29 @@ \subsection{Culture Relevant Coordinate Systems: Zodiac and Lunar Systems}
 The number of entries must be equal to (or larger than) the first element of \jtag{partitions}. Excessive entries are ignored. 
 \end{description}
 
+\noindent In the Arabian peninsula, a similar system of 28 \indexterm{lunar stations} is in use until today, 
+but the actual asterism appears to be more important than the regularity of the ecliptic partition. 
+The first station is centered around \emph{al-Thurayya} (the Pleiades star cluster). In some skycultures the ``band'' of 
+stations around the ecliptic is shown irregular, with boxes trying to frame the associated asterisms:
+
+\begin{jsonfile}[\scriptsize]
+"lunar_system":  { 
+  "name": {"english": "Lunar Stations", "native": "...", "pronounce": "Manazil alQamar", "IPA": "manazilulqamar"},
+  "partitions": [ 28, 3, 2],
+  "extent": [10.0, -10.0, 10.0, -10.0, 10.0, -15.0, 10.0, -15.0, 15.0, ... ],
+    "context": "arabian lunar stations",
+    "link": { "star": 17702, "offset": 6.428571428571429, "comment": "center of first station is Lucida Pleiadum"},
+    "names": [{ "symbol":  "1", "english": "Al-Thurayya", "native": "...", ... },
+              { "symbol":  "2", "english": "Al-Dabaran",  "native": "...", ... },
+                ...
+\end{jsonfile}  
+where
+\begin{description}
+\item[\jtag{partitions}] regular division of the centerline. 28 stations which are further divided into 3 equal parts that are further halved.
+\item[\jtag{extent}] As array of latitude coordinates\newFeature{25.3}, they provide alternating north and south latitudes for all stations. 
+                     The number of entries must be twice the number of partitions.
+\end{description}
+
 \noindent In China, the 28 \indexterm{lunar mansions} are defined in a different way. 28 \indexterm{defining stars} mark the begin (western edge) of each mansion,
 and great circles are drawn from the celestial poles through these stars. In Stellarium, the defining stars are marked with a little circle. 
 The mansions are quite different in width.