A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: What is the Longest Lunar Possible?
From: Brad Morris
Date: 2013 Jan 21, 18:29 -0500
From: Brad Morris
Date: 2013 Jan 21, 18:29 -0500
The best I can offer are my star-to-star sights. I observed Arcturus-Rigel, at just over 135 degrees. Since I made a botch of the refraction correction, there is some doubt as to the precise observation afforded! No doubt on the two stars. No doubt on the magnitude of the angle, its just the final few arcminutes due to my error in the sign of application of the refraction correction.
This Thursday, I plan to the attempt at a 153 degree sun-moon lunar. This occurs right before sunset. Next, I will take a stab at a Polaris backsight, using my view of the Atlantic facing south, at approximately 40 deg 48 min N. I think the reflecting circle should be preset to (90 deg + 49 deg 12 min =) 139 deg 12 minutes. And yes, weather permitting! I read your other post about sailing for years, hoping for clear skies to observe the transit (of Venus), only to see clouds! Fortunately, Polaris is fairly fixed and we can do this experiment whenever the weather clears.
On Mon, Jan 21, 2013 at 4:06 PM, Alexandre Eremenko <eremenko---.edu> wrote:
Brad, I understand the theory. But do you have any actual records of back sights taken with your circle? (My experience with back sights with sextants shows that this is very tricky). Alex. On Mon, 21 Jan 2013, Brad Morris wrote: > > Hi Alex > > 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! > > Best Regards > Brad > On Jan 21, 2013 10:57 AM, "Alexandre Eremenko" > wrote: > >> ------------------------------ >> >> >> 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 >>> >>> >>> >> >> >> >> >> >> View and reply to this message: http://fer3.com/arc/m2.aspx?i=122030 >> > > > > > View and reply to this message: http://fer3.com/arc/m2.aspx?i=122037 > > >
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