A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Brad Morris
Date: 2013 Jan 21, 15:08 -0500
The reflecting circle can take extraordinary backsights. There is a prism attachment for the telescope that puts your head at a right angle to the telescope axis. The prism attachment can rotate about that axis, meaning your body is in a comfortable position, whilst the plane of the reflecting circle is at very unusual attitude. Hence you can measure from slightly less than zero to slightly more than 180 Deg.
There was also an optional stand to completely eliminate fatigue. There is one example of the stand in the Smithsonian. Someday, I will pay a machine shop to make me one!
Brad, > Is there a place on earth where we could observe a lunar distance of ~180 > degrees? This does not depend on the place on Earth. I understand that you want a Lunar which would be impossible with any sextant, but possible with your reflection circle:-) Geometrically, it cannot be exactly 180 degrees, because all large circles intersect the horizon, at the points which are 180 degrees apart. So both the Moon and the star have to be on the horizon, thus invisible. Of course, refraction helps slightly, but this would be a Lunar with both bodies very close to the horizon and this not very accurate. (Notice, in one of the previous discussions we decided that we cannot see Moonrizes and Moonsets over the horizon). But certainly you can try a Lunar of, say 160-165 degrees with your reflecting circle, the thing which is impossible with ordinary sextants. The possibility of the corresponding configuration does not depend on your latitude, btw. You can have it on all latitudes. Once I made a pretty good Lunar at more than 130 degrees with SNO-T, and I think it is near the maximum possible for modern sextants. SNO-T has 140 degrees scale. My pocket sextant has even larger scale, 150, and I tried back sights with it (low Sun and horizon opposite to the Sun), but not with a great success. It is interesting whether you can take a back sight of 160-170 degrees with your circle. Alex. Perhaps in the polar regions, where the sun never sets but skims > the horizon and the full moon simultaneously visible to the observer? > > Would the standard clearing methods work for this lunar? Frank, you warn > of errors when the distance is short, but how about when very long? Would > your calculator work? If there is an error in clearing long distances, at > what angle do we need concern ourselves? > > Lunarians may be familiar with Cook's lunar to 155 degrees. I still don't > understand how he measured this, given his equipment. He didn't have a > circle of reflection, so how did he do it? > > What is the longest lunar distance successfully measured and cleared in > the > log books? Is there any recorded measurement at, say, 160 degrees or > more? > > Regards > Brad > On Jan 21, 2013 1:18 AM, "Frank Reed" wrote: > > > > > View and reply to this message: http://fer3.com/arc/m2.aspx?i=122024 > > >
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