When giving the Time-Altitude formula, I should also mention that sometimes its h answer should be reckoned with respect to north instead of south.
Of course, during the negative-declination half of the year, the sun is always south of the east-west line, and h is always reckoned with respect to south. But, during the positive-declination half of the year, of course there's part of the day when the sun is north of the east-west line. At those times, the Time-Altitude formula's h answer is with respect to north instead of south. Of course that applies, likewise, to the Altitude-Watch approximation to Time-Altitude. So, when using those methods during the positive-declination half of the year, it's best to calculate or estimate when the sun will cross the east-west line. That's so, when the denominator of the Time formula for Az is zero. That's when: cos h = tan dec/tan lat. If you don't have a calculator nearby when you want that answer, you can approximate it by substituting dec and lat for their tangents. ...if the latitude is small, as it is where I reside, in Florida. -------------------------------- I should mention that of course it's often more convenient to multiply by sec Alt than to divide by cos Alt. sec Alt can be estimated directly from the shadow-casting object and its shadow, or it can be gotten from tan Alt, which might be easier to measure, or easier to judge directly from the object and its shadow. Michael Ossipoff On Sun, Jul 19, 2015 at 2:57 PM, Michael Ossipoff <email9648...@gmail.com> wrote: > Barry-- > > Thanks for finding that scene! > -------------------------------------------------------------------------- > > Barry, Sasch & all-- > > Of course Tarzan’s sundial was more for measuring *duration*, rather than > time-of-day. > > > “Get out of the jungle before this duration is up!” > > > I once used a stick Azimuth Sundial for that same purpose, to measure a > duration for someone who didn’t have a watch: > > > My girlfriend at that time and I had been at the beach for some time, and > she was about to go to visit with a group of women who met daily at Carls’ > Junior fastfood restaurant. > > > There was some item at her house (I don’t remember what it was) that she > wanted to have with her when she left the beach. I offered to walk to her > place to find it, and bring it to her at the beach. But, in case I couldn’t > find it, I told her to go ahead and leave for the restaurant after a > certain duration. > > > She didn’t have a watch, and so I made a vertical-stick Azimuth Dial, on a > horizontally-smoothed area of sand, using a thin straight stick as the > gnomon. > > > I marked a small point in the sand, and told her that, if I haven’t > returned by the time the stick’s shadow reaches the mark, then to go ahead > and go to the restaurant meeting, because I couldn’t find the item. > > > I estimated how long it would take me to make the round-trip to her house, > and to find the item. > > > How I determined where to make the mark: > > > I determined it based on a solar direction-finding method that I’ve used > for a long time. I call it the “Altitude Watch Method” (AW), because it’s > an improvement on the familiar “Watch Method” (W), described in so many > books and articles. > > > AW is an approximation to the navigators’ “Time-Altitude Method” (TA). > > > TA says: > > > sin Az = sin h * (cos dec/cos Alt). > > > AW’s approximation consists of assuming that Az and h are > proportionally-related in the same way as sin Az and sin h. > > > At least some of the times when an Altitude Dial based on AW gives its > best estimates of the rate-of-change of Az are when the duration is short > enough so that the sun’s altitude doesn’t change a lot, and: > > > …1) h is small > > > Or > > > …2) the sun’s altitude and the magnitude of its declination are small. > > > But I tested the method, and found it to give good accuracy on the > occasions when I tested it. Maybe those occasions weren’t too far from > solar high noon, and that would explain the accurate results. > > > But, as an approximate measure of duration, where exact time-of-day isn’t > needed, the method should be satisfactory anytime. > > > Though I tested it a few times, I only actually *used* it on that one > occasion at the beach. > > > Michael Ossipoff > > 26N, 80W > > > > > > > > > > > > > > > > > > > On Sun, Jul 19, 2015 at 12:32 PM, Barry Wainwright <bar...@mac.com> wrote: > >> The film is the 1942 “Tarzan’s New York Adventure” and the scene is about >> 6 minutes in. >> >> I’ve uploaded a clip of the scene to You Tube, you can find it at >> https://youtu.be/G-Of5dyGq38 >> >> -- >> Barry >> >> >> >> > On 18 Jul 2015, at 23:29, sasch stephens <sasch...@hotmail.com> wrote: >> > >> > Thanks Michael, you've inspired me to start reviewing Tarzan movies, I >> see that it is a daunting task, there are a lot of them and go back into >> the 1930s. It will be a stroke of luck to find the right one. >> > But for a sundial guy, it's such a special clip. Sasch >> > >> > Date: Sat, 18 Jul 2015 12:28:42 -0400 >> > Subject: Re: Tarzan's sundial >> > From: email9648...@gmail.com >> > To: sasch...@hotmail.com >> > CC: sundial@uni-koeln.de >> > >> > Sasch: >> > >> > The International Movie Data-Base (IMDb) lists 10 Tarzan movies for the >> '50s. >> > >> > But Johnny Weismuller isn't in any of them. It's Lex Baxter (or >> Barker?) until Gordon Baxter took over in 1955. >> > >> > Here's the list: >> > >> > 1950: Tarzan & the Slave Girl (Lex Baxter) >> > 1951: Tarzan's Peril (Lex Baxter) >> > 1952: Tarzan's Savage Fury (Lex Baxter) >> > 1953: Tarzan & the She-Devil (Lex Baxter) >> > 1955: Tarzan's Hidden Jungle (Gordon Scott) >> > 1957: Tarzan & the Lost Safari (Gordon Scott) >> > 1958: Tarzan & the Trappers (Gordon Scott) >> > 1958: Tarzan's Fight for Life (Gordon Scott) >> > 1959: Tarzan's Greatest Adventure (Gordon Scott) >> > 1959: Tarzan the Ape Man (Gordon Scott) >> > >> > Look at the synopses of those movies. Maybe one of them will have >> something familiar from the movie of interest. >> > >> > When you find the right one, or some possibilities for the right one, >> check to find out if it's on YouTube. >> > >> > Michael Ossipoff >> > >> > >> > >> > >> > On Sat, Jul 18, 2015 at 12:16 AM, sasch stephens <sasch...@hotmail.com> >> wrote: >> > There is a Tarzan movie, maybe with Johnnie Weissmiller from the 1950's >> which might have been >> > the inspiration for the Terror Creatures film. I've been hoping to >> find the clip for 30 years to be used as part of a sundial exhibition. It's >> too good! >> > >> > The scene in question finds Tarzan in the jungle with two obviously >> sinister characters near their twin prop plane. Tarzan is telling them >> that they are not welcome there and takes two sticks, one small and one >> large and vigorously sticks them in the ground and says, "When the shadow >> of the tall stick passes the small stick, you must be gone". It fits in so >> well with the primal forces of the jungle. >> > >> > I've been in search of this clip for years, anyone know how to find >> it? Sasch Stephens >> > >> > >> > >> > Date: Fri, 17 Jul 2015 08:47:05 -0400 >> > Subject: Another movie with a sundial >> > From: email9648...@gmail.com >> > To: sundial@uni-koeln.de >> > >> > Another movie with a sundial: >> > >> > A 1965 English-subtitled foreign movie called Terror Creatures from the >> Grave had a character describing and showing a sundial. >> > >> > It was an azimuth dial, admittedly not an old or fancy one. It didn’t >> read in hours. It just marked one solar azimuth. >> > >> > In fact, it consisted of two sticks, vertically sticking in the ground. >> A long stick and a short one. >> > >> > Two characters were walking along the shore, and the woman called the >> man’s attention to something on the ground. He said, “What is it?”. She >> said it was a sundial that her father used to use to find out when the fish >> were biting. When the long stick’s shadow pointed toward the short stick, >> he would take his boat into the reeds. >> > >> > Of course one would expect fish to respond more to solar altitude than >> to azimuth. >> > >> > But there could have been a tree, or a vertical cliff-edge or building, >> that began or ceased to shade the fishing-spot at a certain solar azimuth. >> > >> > Michael Ossipoff >> > >> > --------------------------------------------------- >> https://lists.uni-koeln.de/mailman/listinfo/sundial >> > >> > --------------------------------------------------- >> > https://lists.uni-koeln.de/mailman/listinfo/sundial >> >> --------------------------------------------------- >> https://lists.uni-koeln.de/mailman/listinfo/sundial >> >> >
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