# NavList:

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

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Re: Time Sight usage
From: Robert Bernecky
Date: 2013 Jan 14, 15:36 -0800

He used
hav t = sec L csc p cos S sin S-h
where t is meridian angle, L is latitude of the observer, h is the observed altitude of the body, p is the polar distance. if L and d are same name, p= 90 -d. otherwise p= 90+d
S = (h+L+p)/2

The entries are in the order:
h
L (from the previous day) Log sec L
p (computed a few lines above) Log csc p
2S (h+L+p) Log cos S (# on next line)
S 1/2 of above Log sin S-h (# on next line)
S-h Sum of Logs = Log hav t

the computation is done using log base 10 of the trigonometric functions. You can recreate these numbers by typing into the search window of google. Using Sirius, for example:
10+log ((secant( (5+5.8/60) degrees) )=
10+log(cosecant( (106+38.7/60) degrees))=
and so on... being careful, because it assumes radians for the arguments..
to find the inverse log hav of 8.93916 subtract 10 to get -1.06084. make this the exponent of 10
10^-1.06084=0.0869280625
the inverse haversine is
2*asin(sqrt(0.0869280625)) in deg=

As for the GHA of each star, it looks like he precomputed Aries for 18:17:00 Z added in the SHA, then subtracted 275º and left the remainder as the first number: 51º 49'4 Sirius, and 38º 23'4 Procyon
notice that for the Procyon sight 14 minutes later (ignoring seconds), he adds 3º 30'6 to 275º to get 278º 30'6. I assume he got that from the increments and decrements table for Aries. This is *just a guess*

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