Hello Donald, I suggested you learn by doing it yourself. Sometimes you learn from your mistakes. I made a mistake saying the sine changed to cosine in the southern hemisphere. I realized this error soon after clicking "send" button. For the southern hemisphere, the sign changes + to- but the sine does not change to cosine. The correct equation is Tan HA = Tan T x Sin Lat.
I had in my mind, the concept of horizontal equivalence. For every vertical sundial in the northern hemisphere there is an equivalent horizontal sundial in the southern hemisphere. This is a great concept but not applicable here. Regards, Roger From: Roger Bailey Sent: Wednesday, February 09, 2011 5:59 PM To: Donald Christensen ; [email protected] Subject: Re: part 2 of longitude correction Hello Donald, Three degrees of longitude is 12 minutes of time, 4 minutes per degree, 60 minutes (1 hour) per 15°, 24 hours per 360°. Your longitude is 153 East. You see the sun 12 minutes before the the time zone meridian. Solar noon, when the sun is above your longitude, is 11:48 zone time, on average. To calculate the time lines correctly you have to correct the time angle for each hour line. For solar noon, 11:48, T = 0. For 12:00 Z, T = 3° For 1:00 Z, T = 18° etc as you add 15° time angle for each hour. This is the time angle that you put in the equation for hour angle (HA) to draw the lines. Tan HA = Tan T x Cos Lat. for the southern hemisphere. In the north, it is Sin Lat. If you don't like the trig functions, use one of the standard design packages like Shadows, Zon, Sonne etc. They are simple to use. This is why John C. sent you a drawing. Designing the dial was quicker than explaining the logic. But you only learn by doing it yourself. Regards, Roger Bailey Walking Shadow Designs www.walkingshadow.info From: Donald Christensen Sent: Wednesday, February 09, 2011 2:52 PM To: [email protected] Subject: part 2 of longitude correction I'm laying out lines for a new dial I may not have been clear. I don't intend to rotate the gnomen. The dial will still point true north By labeling 12:12 as noon and 13:12 as 13:00, I am rotating the hour marks. My question is, Is it by an even 3 deg? -- Cheers Donald 0423 102 090 This e-mail is privileged and confidential. If you are not the intended recipient please delete the message and notify the sender. Un-authorized use of this email is subject to penalty of law. So there! -------------------------------------------------------------------------------- --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial -------------------------------------------------------------------------------- --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
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