NavList:

Alan,

To answer your second question, "...how does a star shot [with an AH] work?": The answer is that it works almost the same as using a natural horizon, except with the usual additional step of dividing Hs by two. You see, the stars are so far away from us that they appear as mere points of light with no discernible diameter. When shooting a star with an AH, one overlaps the two images (points). There is no need for a semi-diameter correction because the star appears to us to have no diameter. Therefore, it is as if we brought it down to the horizon, only the sextant will read double the angle, as is usual with an AH.

Incidentally, the same can be done with the sun or moon. Overlapping the two images essentially equates to bringing the center of the body down to the horizon, something that would be practically impossible to do with a natural horizon. Using this method one can bypass the semi-diameter correction for these bodies as well. However, I believe this method is not usually recommended as it is more difficult to discern when the images are precisely aligned as opposed to discerning limb-to-limb contact. My own experience confirms this.

Hope that made sense! :)

Regards,
Sean C.
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