Hello David, Welcome to the list. You have asked an interesting non-trivial question, deserving not just a note but a worthy of a dissertation. Let me add a few thoughts well short of the answer.
Sundials have a prominent but generally ignored role in Muslim culture. Many of our mathematical concepts discovered by the Greeks etc were lost to Europe in the Dark Ages, only to return embellished by the Muslims. There is a good reason why Ptolemy's great book is called Almagest' Like the Mass dials in Europe, the Muslims very early on used sundials to set the times for prayer. Noon, sunrise and sunset were obvious but they observed other times of prayer when the shadow length was one time and two times the height of the gnomon. Old sundials with such markings exist in many parts of the Muslim world. I have see several in Istanbul: The Blue Mosque, Haigia Sophia, Suleiman and the New Mosque. The latter is interesting as there are three dials on the south wall above the foot washing taps. One shows Italian and Babylonian hours with declination lines, the next is a polar axis dial showing typical equal hours. The final one is marked for the times of prayer in the traditional ways. It was interesting to see the evolution of time keeping on this set of dials. Pictures available on request. This doesn't answer your original question, the times that the sun is due east or west. The east west line is easily established with primitive methods like Indian or Hindu Circles, but as you noted, half the year the sun will be below the horizon at these times. This is why I question the interest in a time of prayer when the sun is on the prime vertical, east or west. The usual point of interest for Muslims is not east west but the direction to Mecca. For this you need a Qibla Finder. Arabic astrolabes were designed for this specific purpose. There are many options. While on the subject of Muslim fundamentalism and finding the direction to Mecca, let me mention a controversy brewing in the US over the proposed memorial marking where Flight 93 was taken down on 9/11. People are rightfully outraged that the memorial selected is a red crescent (crescent of embrace) and its axis is pointed at Mecca. What an inappropriate if inadvertent symbol. See http://www.flight93memorialproject.org/crescent_of_embrace.asp for the official story and http://forum.chronwatch.com/forum/viewtopic.php?t=20960 for one of many strong opinions on this subject. Regards, Roger Bailey Walking Shadow Designs N 48.6 W 123.4 -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of David Lawrence Sent: September 16, 2005 1:45 AM To: [email protected] Subject: Is it possible to determine when the sun is due East & West? At first sight, this looked like a 'trivial' request - but it very quickly became apparent that I don't have enough knowledge, and so I have joined this mailing-list in the hope of getting help from people who may be more able to say whether it is even possible! I am located in Northern Ireland, and (knowing of my hobby-level interest in Amateur Astronomy) - I was recently asked if it would be possible to tell the exact time when the sun is DUE EAST & WEST. There is a local group of Muslim 'asylum-seekers', who have been moved here from mainland Britain - and (as part of their religious observance duties), they want to arrange prayer sessions whenever the sun is precisely in both the due East and due West directions. Initially, I thought "Easy - just have a vertical stick (or any simple 'nodus'), with some North/South/East/West markings on the ground, and they can watch the shadow until it shows that time". However, two problems - (1) What if it is not sunny, and (2) Even if it is sunny, what would they do during the Winter period, when the sun will rise/set without reaching the East/West directions? My next thought was "OK, it should be possible to use a computer program to calculate the times, for every day of the year" - BUT the Muslim group will not accept any form of 'modern technology' for this task, and insist that it must be done either by direct observation or obvious mechanical means (apparently some type of simple 'clockwork' will be OK for them, but nothing electronic). My question is therefore "Can the moment when the sun is exactly due East or West be determined, in any way which will satisfy this 'fundamentalist' Muslim group - or is it an impossible request? Any thoughts or suggestions from members will be much appreciated. Sincerely, David Lawrence. -- - -
