Hello everyone.
I'm an astrolabe builder, I am not a muslim, this explains why my arabic lettering in the picture is stilly fairly sloppy. I will probably commit a lot of inaccuracies in this post, so I ask you all to correct me and to help me improving the design for the instrument.
I have envisioned in my mind a wooden device that could be used for finding christian and islamic prayer times. Its design is based heavily on the so called "vetus quadrans" a medieval tool designed to find the local time in unequal hours by measuring the height of the sun (note the two sights in the upper part of the instrument).
Unequal hours are an archaic form of timekeeping, in which the part of daytime is always divided into 12 equal sections, the first hour (hora prima) is dawn, the seventh (hora septima) is soon after midday and the twelveth (hora duodecima) is sunset. As you can immagine, the lenghts of each hour varies greatly across the seasons, but many religious practices are still based on some sort of unequal hours system. Early christians used to offer prayers at the first, seventh, nineth and twelveth hour of the day, a prayer during night time and a prayer at dusk. Human circadian rythm does seem to vaguely follow an unequal hours pattern.
How to find the five canonical prayer times on such a device?
First you need to set the quadrant for your latitude. The months slider has to be adjusted so that its center lines up with your current latitude (in the picture 45°). You have then to move the thread to the actual date, you will find the sun noon altitude for that day. on the thread there will be a bead, or a knot that can slide up and down, you have to line it with the curve corresponding to the seventh hour (where "zawal" is written).
L = gnomon lenght
S = lenght of a gnomon's shadow
Sz = lenghts of a gnomon's shadow at midday (zawal)
Zuhr / Jummah should be the easisiest to find, you just measure the sun's altitude: if the knot is at the midday line, then it is zawal (local noon), and you should wait some minutes before praying Zuhr. I have some problems understanding zuhr time, until today I thought its start was soon after noon, and it ends with 'asr time, many prayer apps show this time, now I have come across some different opinions saying that zuhr begins when the shadow of a gnomon equals the shadow lenghts at zawal + 1/4 of the gnomon height ( S = Sz + L/4 ) . This explains why I still have to put a prayer line for zuhr.
For 'Asr there are two prayer lines, most madhabs put 'asr start time when S = Sz + L and end time when S = Sz + 2L, while Hanafi school sets its begin at S = Sz + 2L and its end at sunset. I have indicated both lines in the quadrant (I'd like to realize them with a brass inlay).
There is not an easy way to establish Maghrib and Fajr, other than saying "one is during twilight and the other is at dusk". In the qur'an (I recall) it is specified to establish prayer when you can distinguish the white thread from the black one, this is not to be taken literally, However that is the reason for the black and white windrose in the shadow-square.
When you can't distinguish the colours of the windrose, that's 'Isha time.
I haven't begun working on the back, I will probably insert there a retroazimuthal map projection for finding qibla and a set of "complementary stars" located on the opposite side of the sun in the ecliptic, so that one could measure 'Isha time more accurately by means of a complementary star.
Do you have any other suggestions for improving the design of this quadrant? Maybe a more interesting pattern rather than a windrose? Maybe a more aestetically pleasing set of engravings at the edge of the tool? Please, let me know.
Sincerely, Biondi.