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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Refraction.
From: John Brenneise
Date: 2004 Jul 9, 11:14 -0700
From: John Brenneise
Date: 2004 Jul 9, 11:14 -0700
I'll buy most of what you said in your
previous post. In it you state:
"In normal air, the index is
1.0003, so if the air is 5% denser, the index would be about
1.000315".
Implicit in this statement is the assumption
that the relationship between the increase in density and the increase
in the index of refraction is linear. Can you give me a reference
about this?
I believe that a correllation is there,
but if the functional form is linear, then is the constant of
proportionality exactly 1.0? If it is non-linear, then what is the functional
form?
John
----- Original Message -----From: Frank ReedSent: Friday, July 09, 2004 1:57 AMSubject: Re: Refraction.I wrote earlier:
"So the net refraction (standard plus the weather front) is 4" of arc TOWARDS the zenith on one side of the zenith and 2" of arc AWAY from the zenith on the other side.
Make sense?"
Did that resolve the matter for everyone, or no? John B, does that make sense for you? You asked for a specific example (but that post more or less coincided in time with the above example so you may have missed the details). The conclusion is YES, the net refraction CAN place a star's apparent position lower in the sky than its true position, but rarely and not by much.
By the way, I don't think temperature inversions (plane parallel) make any overall difference (that is, they can't make the net refraction opposite in sign from the standard refraction); if the atmospheric density is plane-parallel, the net refraction always puts the apparent stars above the "true" stars.
Frank R
[ ] Mystic, Connecticut
[X] Chicago, Illinois
