NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Extremely poor conditions??
From: David Fleming
Date: 2012 Mar 21, 13:33 -0400
From: David Fleming
Date: 2012 Mar 21, 13:33 -0400
Yes, I agree as my prior statement retracted the statement about equality.
Still terrestrial refraction results in rays with a center of curvature toward the earth.
Additionally the increase in air density due to cooling effect of the water will increase that curvature further raising the apparent position of the horizon giving the results obtained in your meazsurements
On Wed, Mar 21, 2012 at 1:24 PM, Alexandre E Eremenko <eremenko@math.purdue.edu> wrote:
David,No. The first statement does not imply the second. Just look at the Almanac table for the dip.
That is the sun LL is seen 30 min higher in sky than it is.
This means that usual conditions also raise the apparent horizon by the same 30 mins or the visible horizon is further than the geometric horizon.
The reason is that the ray from the Sun travels through the whole
atmosphere (so it has plenty of time to get distorted by 30')
But the ray from the horizon travels to our eye only few miles.
So this second ray is distorted much less.
As the dip table in the Almanac shows.
Alex.
