Hello David, I believe that I can offer a method that "might" meet the requirements of this group. However, it will depend upon the clarification of a couple of points. What do the terms "exact" and "precisely" mean in this case? What deviation, if any, is allowed? And can "modern technology" be used to create the device that would be used to give the required information? Modern technology would most likely be used to create any simple "clockwork".
My suggestion and its limitations are as follows. I have a device on my web site called the "Dialling Buddy". You can get a pdf file that allows you to build this device at the following address: www.mysundial.ca/sdu/sdu_dialling_buddy.html Once you have built the device all you have to do is set the arrow to the latitude where it will be used. The times when the sun is due east and west is indicated at the "Vertical Wall". The day is selected by using the "Date Ruler" and lining it up with the date lines at either end of the transparent plate. All that is required is a mechanical timepiece such as a pendulum clock set to indicate local apparent or solar time. There are some limitations to this method. The placement of the date lines for a device of this scale is at five day intervals and the time intervals are 15 minutes. This is probably inadequate. The position of the date lines is determined by the sun's declination on a particular day. This value changes slightly from year to year and will introduce a slight error. February 29 is not even shown. Is this a problem? If the device was increased significantly in size, say 24 to 36 inches across, it might be possible to have one day and one minute intervals. For a large device the transparency material used for the top rotating plate could be replaced by plexiglas. The plexiglas could be permanently fixed at the latitude where the device is located. A straight edge would be aligned with the date lines of the day of interest. The times when the sun will be directly east and west would be recorded. The device could be mounted on a wall next to the pendulum clock. The clock would be used to tell you when these times have arrived. Once this device was designed to meet the group's requirements it could be used anywhere. All you need to know is the latitude. One other potential problem is that you would probably like to use a computer to design the device and some sign making technique to ensure an accurate device. If you purchase a mechanical clock this would also be an issue The accuracy of the mechanical clock would also have to be considered. I hope that this helps. Regards, Carl Sabanski www.mysundial.ca -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of David Lawrence Sent: Friday, September 16, 2005 3:45 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. -- - -
