# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: formula for refraction
From: Dave Walden
Date: 2007 May 01, 20:33 -0700

```The following short FORTRAN program reproduces the critical table for
refraction from the NA.  It is NOT based on fitted equations.  It uses
the canonical multilayer-ray-following method of Biot-Auber-Standish
(Astronomical Journal,119,2472-2474,2000 May).  It calls the slREFRO
program of Wallace based on the work of Hohenkerk (HMNAO. Sept 1984).
http://stsdas.stsci.edu/cgi-bin/gethelp.cgi?refro.hlp
You can change pressue, temp, humidity, etc to generate your own
table.

program dwrefracna
implicit none
real*8 ZOBS,HM,TDK,PMB,RH,WL,PHI,TLR,EPS,REF
real*8 pi,xi,rlim
print*,'from dwrefracna.f'
pi=4.d0*datan(1.d0)
print*,pi
hm=0.d0
phi=45.d0*pi/180.d0
c na 2007 values
tdk=273.15d0+10.d0
pmb=1010.d0
rh=0.80d0
wl=0.50169d0
c assume tlr .0065
tlr=0.0065d0
eps=1d-10
rlim=+5.35d0
do 4 xi=9.d0,90.d0,1.d0/60.d0
zobs=pi/180.d0*(90.d0-xi)
call slRFRO(ZOBS,HM,TDK,PMB,RH,WL,PHI,TLR,EPS,REF)
ref=ref*180.d0/pi*60.d0
if(ref.lt.rlim)then
print'(i3,f4.0,f8.5)',int(xi-1.d0/60.d0)
&       ,60.d0*(xi-1.d0/60.d0-int(xi-1.d0/60.d0))
print'(8x,a1,f3.1)','-',rlim
rlim=rlim-.1d0
endif
4   continue
end

from dwrefracna.f
3.14159265
9 55.
-5.3
10  7.
-5.2
10 20.
-5.2
10 32.
-5.1
10 46.
-5.0
10 59.
-4.9
11 14.
-4.8
11 29.
-4.7
11 44.
-4.6
12  0.
-4.5
12 17.
-4.4
12 35.
-4.3
12 53.
-4.2
13 12.
-4.1
13 32.
-4.0
13 53.
-3.9
14 16.
-3.8
14 39.
-3.7
15  3.
-3.6
15 29.
-3.5

etc.

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```
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