k k k i was reading this and reflected on somma my learning from very astute instructors and began to laugh while reading this piece ~ By Quintus Twig The last point under Observe Nature is somewhat misleading. The sun is at true South at local noon, not mean noon. The difference is that mean noon is the time at which the sun is highest in the sky at the standard meridian for the time zone (the meridian of longitude that passes through the center of a time zone and is used to standardize time in the entire time zone) while local noon is the point at which the sun is at the highest point in the sky for the exact location. There can be as much as a half-hour difference between mean noon (1200 at your time zone) and local noon. Thats as much as 7.5 degrees in the wrong direction. Heres what I recommend: Gather a standard-sized sheet of paper, a drawing compass, tape (scotch tape is fine), a short nail (less than an inch long), a pen or pencil, and a clipboard. Stick the nail through the center of the piece of paper and record your location and tomorrows date (or whenever you use this device) at the edge of the paper. Clip the paper onto the clipboard (with the nail standing vertically) and tape the loose end of the paper to the clipboard so that the paper has no wrinkles (!!!). Then get a good nights sleep (especially if you are doing this in the summer). Be prepared to record the position of the nails shadow every hour or so (the smaller the intervals the better). Set the clipboard (with paper and nail) on the ground outside (in a sunny spot) before ten oclock am at latest (if you record the shadow at very short intervals, then you could probably start at eleven, but any later and it defies the purpose). Mark the point of the nails shadow at whatever interval you choose (hour is sufficient if you dont need great precision) and record the time for each. Keep recording until after one oclock (or if you want a complete plot, keep going until the shadow fades away; these plots can be useful for those interested in astronomy as I will explain). Now trace your plot (for an astronomically useful tracing, try to trace the curve). A good record should show a U that approaches the nail. Remove the nail (without shifting the paper or clipboard!!!) Take the drawing compass and draw a circle around where the nail was. Draw a line between the two intersections of the circle and shadow plot. Find the middle of this line, draw a line from this point to where the nail was. This line points south (true south). This is the astronomical definition of south. The plots can be used to predict the motions of celestial bodies by calculating the altitude of the sun from the shadow plot. Measure from a point you marked to where the nail was and record that distance as a variable, B. The equation for altitude is as follows: A = arctan (C/B) where A is the altitude and C is the nails height Observe how the planets move in comparison with the line formed between the sun at the altitudes by mentally pulling the shadow plot inside out and imagining it in the sky (at the calculated altitudes). While standing near the clipboard (right next to it), find visual references for yourself (I use branches of trees). Then you can watch the stars move in relation to this imaginary line (I wont spoil it for you!). The method of making shadow plots to find south is quite accurate. I have used it to create several sundials, all of which were quite accurate (within ten minutes of my watch). This is more accurate than sighting polaris (the North Star, which actually deviates slightly from North in a circular pattern) and I strongly advise anyone interested in astronomy to study shadow interpretation (gnomonics) and dialing (theory and construction of sundials, which are more complicated than they seem). ...just as a mahu would have explained soooo explicitly and i shall say how familiar mahu is to kahu k
Posted on: Thu, 31 Oct 2013 19:40:17 +0000
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