NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Martelli's Time-Sight Tables
From: Hewitt Schlereth
Date: 2012 Dec 23, 20:15 -0800
From: Hewitt Schlereth
Date: 2012 Dec 23, 20:15 -0800
Greg - Hey, great going. Never in my life did I think of trying a moon time sight. Exotic, man. This afternoon I looked in Vol. i of my green Bowditch and it gives Martelli' formula as: havt = cos(L~d) – cosz / 2cosL cosd Since havt = (1– cost ) and z = (90* – h) I rewrote the formula to: cost = 1 – (cos(L~d) – sinh / 2cosL cosd) With the formula now in sines and cosines, I plugged Martelli's example into a basic scientific calculator, but got an answer that was way off. So, I went through and wrote down the results from each operation. At which point I noticed the final number was half the cosine of the angle I was looking for. So, I took the 2 out of the divisor and did it again. The result agreed with Martelli to 0.1'. So, I think the formula is cost = 1 – (cos(L~d) – sinh / cosL cosd) Greg, when you can spare the time, could you check me out on this? It's been a long time since I messed around with equations. Thanks, Hewitt Sent from my iPad On Dec 23, 2012, at 5:59 PM, "Greg Rudzinski"wrote: > Hewitt, > > Using Frank's Martelli PDF I was able to do a Moon time sight this evening to near perfection. The tables are easy to use but I do not like working in hours, minutes, and seconds when LHA could be given directly saving several steps. > > Here is how the formula may compare to the tables: > > ArcCos[ (SinHo ~ SinLSind) / (CosLCosd) > Tab#V Tab#III Tab#II Tab#IV Tab#I > > > Greg Rudzinski > > > [NavList] Martelli's Time-Sight Tables > From: Hewitt Schlereth > Date: 22 Dec 2012 19:12 > I ordered this book from Amazon and it came yesterday. Full title is "Short, > easy, and improved method of finding the apparent time at the ship." > > It's a trade paperback, and I have to say Hewlet-Packard made a nice job of > it. The signatures are stitched, so they shouldn't come loose. The only > shortcoming with my copy is the print on page 42 and pages 44 thru 47 of > Table V is light (but still quite legible). > > The tables are I thru VI and the method takes them in that order. What you end > up with is LHA expressed in time units, so you have to convert to the angular > units we are used to- 1 hour = 15*, 4 mins = 1* ... > > After working through his English example (the same data is used for > directions in French, German, Italian and Spanish), I ran the example through > my HP 35s using the sine/cosine formula and it gave an answer 1.0' less than > Martelli. > > Then I tried M's table with Greg's 12-17 time sight and again the difference was 1.0'. > > My 1972 Bowditch noted that Martelli's method was still popular. Having been > an active navigator then having tried it now, I can see why. There are 6 > tables, but they are short and logical. In neither of the cases I tried did I > have to do an interpolation. > > My one cavil is to wish M had set out the formulas he used. I have the same > gripe about the Concise SR table in the NA. > > Net of everything, though, Martelli's book is an agreeable stocking stuffer for myself. > > Hewitt > > ---------------------------------------------------------------- > 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 > ---------------------------------------------------------------- > > > > > : http://fer3.com/arc/m2.aspx?i=121534 > >