A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: David Pike
Date: 2020 Jul 27, 04:34 -0700
The attached photos show an AH which I find perfectly adequate for my ‘Boy Scouts’ form of celestial. Most of the bits are available from eBay for a couple of £s. A front surface mirror would be the ‘icing on the cake’, but beggars can’t be choosers. It’s not dissimilar to the standby AH Amundsen took to the South Pole in case his mercury froze. It didn’t; he was lucky with weather. If you’re intending to work from a back garden, you need to think about the height to place the A/H. For low Hs observations from a low placed AH in the average back garden, it wont be long before you’re backing into the house wall before you can be comfortable and be able to see over the garden wall at the same time. Chest height would make best use of the space available but would be more liable to instability. Do the diagrams.
Sudden bright idea, which I’ve only just thought of and fortunately can’t test because it’s overcast and raining. Assuming your sextant is properly adjusted, and you’re holding it vertically, if the two Suns or stars don’t coincide laterally, it must be due to the mirror being tilted sideways. I have experienced this. Therefore, ensure one adjusting screw is in line with the body to be observed. Pick a cloud or star at 90 degrees to the body you’re trying to observe. If the two bodies don’t coincide laterally, tweak the fore and aft screw until they do. The mirror should now be horizontal in the direction of the body to be observed. With three equally spaced adjusting screws, this would be ideal for fine levelling for 3PL fixes. Alternatively, stick to 2 PLs, and no one can criticise your cocked hats. DaveP