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Re: Irradiation
From: Bill B
Date: 2004 Nov 28, 21:35 -0500
From: Bill B
Date: 2004 Nov 28, 21:35 -0500
> on. Now I guess that I am doing the right thing but for the > wrong reason. Although this leaves me with a question now, can I shoot the > stares with a horizon illuminated only by the moon? Robert Bruce Bauer (The Sextant Handbook) suggests, if I am reading him correctly, that if you are badly in need of a fix, make the observation over the suspect moonlighted horizon with the darkest shade feasible. (I believe he is addressing the moon as the observed body as he later goes on to talk about stars.) Then set the sextant at its current index correction to make the reflected horizon level with the true horizon. Then remove the shade(s) and aim at the moonlit horizon excluding the moon from the field of view. View the side areas where the reflected moonlight trails off into obscurity. There may be a "jump" up in the level of the moonlit horizon due to irradiation. Examine the the edge of the elevated horizon vs. the lower horizon with the lightest possible shade, and adjust the micrometer drum until the elevated and true horizon are level. Use this difference as an adjustment factor. Finally, compare both the original and adjusted (reduced?) versions and compare to your DR, and make an educated guess. In the case of stars, it is about the same deal. Bauer suggest checking the horizon with 7 X 50 wide-view binoculars to look for a possible horizon jump due to irradiation. Hope that helps, Bill