# NavList:

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

**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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