# NavList:

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

**Re: Time Sight usage**

**From:**Henry Halboth

**Date:**2013 Jan 14, 20:46 -0500

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)/2The 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 tthe 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*----------------------------------------------------------------

NavList message boards and member settings: www.fer3.com/NavList

Members may optionally receive posts by email.

To cancel email delivery, send a message to NoMail[at]fer3.com

----------------------------------------------------------------View and reply to this message: http://fer3.com/arc/m2.aspx?i=121948