NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Star - Star Observations
From: Peter Hakel
Date: 2010 Mar 10, 09:06 -0800
From: Peter Hakel
Date: 2010 Mar 10, 09:06 -0800
George, here is the essential part from Brad's original posting.
"Because each object is on either side of my zenith, both objects will appear to be lower in the sky compared to the horizon, due to refraction. Yet because they oppose each other in azimuth, the observable distance between them should be larger by the sum of the refraction corrections, not reduced by the difference of the refraction corrections."
Brad has since clarified that he was interested in the general case, which of course does need full spherical trig, just as you pointed out.
Peter Hakel
From: George Huxtable <george@hux.me.uk>
To: NavList@fer3.com
Sent: Wed, March 10, 2010 3:38:50 AM
Subject: [NavList] Re: Star - Star Observations
Let me try to summarise the current state-of-play, following Brad's initial
question about predicting corrected star-star distances, for calibrating an
instrument.
Unfortunately, Brad didn't make it clear whether he was considering the
trivially-simple case; the angle between two stars, at a time chosen so that
they have the same, or opposite,azimuths, as has recently been discussed on
the list. Or the more general case of the angle between two stars wherever
they happen to be in the sky.
Peter Hakel (I think wrongly) presumed the former, and provided a short and
simple comment, which I wrongly took to imply his committment to the
procedure Brad had suggested.
[rest deleted by PH]
"Because each object is on either side of my zenith, both objects will appear to be lower in the sky compared to the horizon, due to refraction. Yet because they oppose each other in azimuth, the observable distance between them should be larger by the sum of the refraction corrections, not reduced by the difference of the refraction corrections."
Brad has since clarified that he was interested in the general case, which of course does need full spherical trig, just as you pointed out.
Peter Hakel
From: George Huxtable <george@hux.me.uk>
To: NavList@fer3.com
Sent: Wed, March 10, 2010 3:38:50 AM
Subject: [NavList] Re: Star - Star Observations
Let me try to summarise the current state-of-play, following Brad's initial
question about predicting corrected star-star distances, for calibrating an
instrument.
Unfortunately, Brad didn't make it clear whether he was considering the
trivially-simple case; the angle between two stars, at a time chosen so that
they have the same, or opposite,azimuths, as has recently been discussed on
the list. Or the more general case of the angle between two stars wherever
they happen to be in the sky.
Peter Hakel (I think wrongly) presumed the former, and provided a short and
simple comment, which I wrongly took to imply his committment to the
procedure Brad had suggested.
[rest deleted by PH]
