NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Moon sight?
From: Stan K
Date: 2014 Oct 5, 18:20 -0400
From: Stan K
Date: 2014 Oct 5, 18:20 -0400
FYI, the refraction formula in the back of the Nautical Almanac was the Bennett formula,
R (in arc minutes) = 1/tan (H + 7.31/H + 4.4),
through the 2004 Almanac. In 2005 it changed to
R (in arc minutes) = 1/tan (H + 7.32/H + 4.32).
Interestingly, the altitude correction tables at the front of the Almanac reflected this change in 2004. Not changing the formula in 2004 was apparently just an oversight.
FWIW, this change only affects the refraction value for apparent altitudes of about 2º or less.
Stan
-----Original Message-----
From: Bill B <NoReply_BillB@navlist.net>
To: slk1000 <slk1000@aol.com>
Sent: Sun, Oct 5, 2014 4:52 pm
Subject: [NavList] Re: Moon sight?
From: Bill B <NoReply_BillB@navlist.net>
To: slk1000 <slk1000@aol.com>
Sent: Sun, Oct 5, 2014 4:52 pm
Subject: [NavList] Re: Moon sight?
On 10/5/2014 12:31 AM, Sean C wrote: > Would you please explain to me the formula you use for Refraction and > where you got the figures? The 7.32 and 4.32. Sorry about the my answer. Off base as I commingled two of my projects in my memory. The 7.32 and 4.32 are very similar in value to those used in Bennett's simple formula on page 106 of Meeus's "Astronomical Algorithms," but the formula's differ. Bennett's formula is: R (in arc minutes) = 1/tan (ho + 7.31/ho + 4.4) ho = apparent altitude = Ha Bennetts's formula from Wikipedia http://en.wikipedia.org/wiki/Atmospheric_refraction R=cot(ha + 7.31/ha+4.4) As Bennett's is referred to as a "simple empirical formula," and Bennett gives two methods of refining the results, I would surmise the NA version is more rigorous. Bottom line, this does not answer you math/physics question of how the constants and formula's were derived. Some of the list Guru's may help out there.
