Moslem sundials were generally constructed with a view to determining the correct time for prayers rather than dividing the day into equal parts. Most of the prayer times are easily determined by observation with minor refinements like inability to distinguish a black thread from a white one at sunset. The prayer times are: Fajr - dawn Dhuhr - midday Asr - mid-afternoon Maghrib - sunset Isha - night The two times that present difficulties, and where the sun's shadow comes into play, are Dhur, midday and Asr, mid-afternoon. Asr is particularly problematic because it is defined by a rule -- and there are variants depending on the sect -- relating the length of an object's shadow and the length of its shadow at noon. It is harder to estimate than Dhur if only because at Asr the length of the objects shadow at midday is no longer directly observable. Asr is usually marked clearly on islamic dials like the ones in Turkey. The other thing of interest is sometimes how much daylight is still left before Maghrib The photo seems to show a stone tablet propped up on blocks of some sort inside the building. Is there any indication of how the sundial -- if it is one -- was originally situated? Horizontal or vertical? I have actually visited the mosque in Xian many years ago but did not see a dial. If it had been accompanied by a plaque I think I would have certainly noticed it. I did, of course, see the unremarkable dial in the Forbidden City, which looks like an import from the West, and have always wondered why the Chinese did not seem to have felt any need for sundials. The layout of the holes with widely and closely spaced marks suggests that it may have been a variation on a polar dial designed to start at midday. For most latitudes a vertical object casts a shadow at noon and a normal polar dial would not be appropriate, since there is a requirement for a midday shadow length. This might have been a “horizontal- polar” dial. The first set of single marks might have been the length of a dhur shadow at different months and the second set of (double) marks might have been Asr for different months. Or maybe it was designed for a movable gnomon. This is all completely speculative with no serious model to figure out if it is even plausible. If anybody is going to be visiting Xian it would be worthwhile to take some photos that could be used to count the marks more clearly and figure out their spacing. With accurate measurements, it may be possible to figure out. Or maybe there is somebody in China who has already figured it out. Jack Aubert From: sundial <[email protected]> On Behalf Of [email protected] Sent: Tuesday, January 5, 2021 9:23 AM To: [email protected] Subject: Strange sundial in China Hi group, I saw this sundial in the Xi'an Mosque in China. Can anyone tell me how this sundial worked? Clear skies, 🔭 Gerard van den Braak <http://www.sterrenwacht.eu/> www.sterrenwacht.eu <http://www.zonnewijzers-nederland.nl> www.zonnewijzers-nederland.nl
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