I have not been able to figure out a plausible way to contort my watch arm so that 12:00 noon faces my body. You lost me at step 1.
Jack Aubert -----Original Message----- From: sundial-boun...@uni-koeln.de [mailto:sundial-boun...@uni-koeln.de] On Behalf Of Will Vaughan Sent: Tuesday, October 18, 2011 7:58 PM To: sund...@rrz.uni-koeln.de Subject: Re: a reverse sundial for the blind "Reverse sundial" is a clever phrase to describe the Boy Scout method of finding north (which I call "Seton's rule" after the organization's founder), since Seton's rule gives the wrong direction in general for the same reason that an uninclined equatorial sundial tells the wrong time in general: the Sun's motion is usually not parallel to the horizon, so the Sun's hour angle is usually not equal to its azimuth (plus a constant). It seems to me, however, that if you inclined your watch, you could use it as an equatorial sundial and more accurately find north. Here's a method that might work (but that's also unfortunately less pithy than Seton's rule): 1) Incline your watch arm at the local latitude (note: I can't say "in the N/S plane"; this is the tricky part). Assume 12:00 noon on your watch is facing your body. 2) Split the difference between the current time and 12:00 noon on your watch. The angle between this halfway point and 12:00 noon is the hour angle of the Sun. 3) Awkwardly bend your other arm so that it's sitting on your watch-wearing arm and pointing towards this halfway point. 4) Rotate your body until you can feel the sun on your bent arm. (You may have to tilt your hand if the declination of the sun is extreme). 5) Now 12:00 noon on your watch wearing arm faces south. If you have the watch-wearing arm held out straight in front of your body you should be facing north. If you're sighted, steps 3) and 4) are easier: hold up a finger normal to the watch dial and use it as a gnomon; rotate until your finger's shadow is opposite the halfway point. Will --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
