NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Brad Morris
Date: 2012 Dec 14, 19:09 -0500
Hi John
I see now. The table presented presumes you know the altitude of the objects (stars). I started one step back from there and determined altitude using direct computation. So we are in agreement there.
I do note the rather small correction as the altitudes vary for this pair. I expect that to be a function of the small distance between them, the small correction for refraction and the way in which the corner cosines adjust that correction. The table has a cleared distance, all the person must do is measure!
A more general equation can be made for any interstellar pair. For this, all the steps in determining altitude, expected refraction at altitude, corner cosines (clearing the distance) must be performed. That is, I should be able to preset the exact distance for any pair, by precomputing it from stellar positional data.
Its not just one pair I desire. Its a series of pairs that can span the range of my instrument, such that I can calibrate the arc. How large is my arc you ask? Just a few degrees more than 180 on my Circle of Reflection (shown at NavigationWeekend 2010). So basically horizon to horizon.
I have made rather of fudge of this in the past, but remains a topic of high interest to me. So forgive my enthusiasm. I surely have the calibration of this arc as a lifetime goal
Best Regards
Brad Morris
I
Brad,
I'm not quite getting your point. I've attached one star-star table for discussion. It's to be entered with the altitude of each star at the time of the star-star distance sight. So there's no question of moving stars or time of observation.
The concept is valid for all altitudes, even down to zero. Of course there's additional corrections for non-standard temps and pressures. But I've only tabulated down to 15d altitudes because of the poor observations at these lower altitudes -- not because of any limitations in altitude corrections.
Note how small the "clearing" corrections are and how insensitive they are to the altitudes.
John
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