On Thu, 23 Sep 1999, Planocka Vit wrote: > I have recently noticed an offering on ebay.com of an interesting > device, a solar slide rule that should predict the time and azimuth > of the sunrise and sunset for a given location. (I actually think > that it shouldn`t be called a slide rule, just a nomogram). > > I saved a copy of the short description and images at: > > http://www2.crosswinds.net/~vitplanocka/ebay.htm > > Could someone please tell me something about the principle of this > device? > Vit Planocka > 50N 15E
Neat little device! I'm just working from the pictures here, but it looks very straight-forward. The front is a flattened globe, and is only used to look up your latitude and longitude. Rotate the cursor disk so the radial line crosses your location. Look up longitude on the outermost blue scale - lots of resolution, there. (You also see your time zone, and can use the outer red scale on the disk to look ahead or back some number of hours). Your latitude is where the radial line hits your site. Flip over onto the back, and set your longitude (or what you read 'n' hours ahead or back of your actual longitude) against the date, on the outer blue scale. Look where your latitude on one of the radial red lines crosses a curve, and follow that curve to the inner or middle blue scale. One radial line-and-blue scale combination reads in Azimuth, the other in Hours. (not sure whether 'time of day' or 'hours to go'.) I think all the real "work" is embedded in the wavy lines on the back. I'll let one of the spherical trig gurus figure out how to program that into an Excell spreadsheet! Dave
