Warren Thom wrote: > > Hi All, > I printed out a horizontal dial for my 87 year old father. I make > it with Zonwvlak (available from NASS). After reading the directions, > I found the software powerful yet easy to use. F.J. de Vries did an > excellent job in writng the software. I found that Ami Pro 3.0 will > import a picture in the .plt format under HPGL as the choice format. > The aspect ratio is maintaind and it prints to a full sheet of paper. > I had a minor problem using the draw program (Scrplt) because I could > not always remember the file name that I had created. > > Now for a few general questions. > > Babylonian hours. I take it these are the lines for each hour > since sunrise. I also assume they are each 1/24 of a day long. > Are they numbered from sunrise, with sunrise=0, one hour later as 1 > two hours since sunrise as 2 etc? > > Italian hours. I understand these to be the hours until sunset. > I would take these to also be 1/24 of a day in length. Is sunset=0 > and one hour before sunset=1, etc? > > What exactly is a bifilair sundial? I take it that it has two planes > perpendicular to each other. If so why does Zonwvlak only print one > surface? No wait....reading.....does a bifilair dial use the lines on > a transparent surface to be read with one point where the "shadows" hit? > > Now for a math question. In analytical geometry the equation of an > ellipse is: (with the origin at the center and semi-axes a and b) > > (X**2/a**2) + (y**2/b**2) = 1 (**2 means squared) > > the equation of a hyperbola is: > > (X**2/a**2) - (y**2/b**2) = 1 > > Can we draw a sundial from these equations? How are a and b related to > latitude, declination of the sun, and hour angle? This will keep me off > the streets and out of trouble for a while. > > Sincerely, > > ********************************************************************* > Warren Thom [EMAIL PROTECTED] or [EMAIL PROTECTED] > Hompage Still working on it. > *********************************************************************
Warren Thom, Thank you for your remarks about my computerprogram. Babylonian hours are counted from sunrise and an hour is equal to our hour. You can also read them as "how long the sun did shine this day" Italian hours are counted from sunset. 1 It. = 1 hour after sunset. Subtracted from 24 you can say "how long the sun still will shine this day" A bifilar dial has two threads as shadow casting device. The threads are of different height above the dialplate. The dial is read at the crosspoint of the shadows of the two threads. In my program one thread is parallel to the x- axis and the other to the y- axis. This is not the normaly used bifilar dial. There one thread is parallel to the equinoxline (but not direct above that line) and the second perpendicular to the first one. In this last case it is possible to make a dial with equiangular hourlines. But at the time I made my programs I didn't know that. I am sorry, I can't help you with the analytical formulas. In that way I have no experience to calculate a sundial. I wish you many sun and happy dialing. Fer de Vries, Netherlands.
