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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Peter Monta
Date: 2019 Dec 7, 23:58 -0800
That's what I did, the few times I have tried to observe star separation angles. A steady superimposition of both bodies doesn't work for me. To my eye it makes the error more difficult to perceive. I prefer to repeatedly sweep one star past the other.
Coincidence of images of a star, however, may be observed with very great nicety; and if we select for the purpose a bright one, and make our observations of coincidence when this first becomes visible in the twilight, we shall find a number of readings rarely exhibiting a difference of more than 3 or 4 seconds between the extremes. This then is the method I am inclined to recommend; and on repeating the operation in the course or at the conclusion of a series of observations, should the sky have darkened in the meantime, a star of inferior magnitude may be taken for the purpose, but still not so small as to occasion any unpleasant exertion of the eye to perceive clearly the coincidence of images. The coincidences should in all cases be made by alternately elevating and depressing the reflected image, so that, the first being obtained by elevating the reflected image, in making the second we should depress it, and so on. The mean of an even number of readings, not fewer than eight, will, I believe, seldom differ 1" from the truth.