Tuesday, November 29, 2016

Quicker Ex-Meridian Formula

This modified ex-meridian formula saves a few moves on the K&E slide rule (solution time 50 seconds).

Slide Rule:

a = (Cos Lat. Cos Dec.) / Sin (Lat. +/- Dec.)***      
(+) contrary name  (-) same name  *

+XM' = .524 (a)(t)(t)      
t = meridian angle in degrees and tenths  **

Calculator:

+XM' = (a)(t)(t) / 1.91

notes:

 * The (a) value can be worked up prior to observation. 
** Slide rule tip - pencil mark the slide C scale at .524 for quick cursor set.
*** Cos (Ho) can be substituted for Sin (Lat. +/- Dec.)   Ho = corr. sextant altitude

+XM' = ex-meridian minutes of arc to be added to Ho then solve as a LAN observation.


Sunday, September 4, 2016

Ex-Meridian by Slide Rule




The ex-meridian calculation can be performed faster by slide rule than by pocket trig calculator with equal precision for celestial navigation purposes. 5 moves of the cursor and 6 moves of the slide in less than 2 minutes of time.

http://gregrudzinski.blogspot.com/2011/01/ex-meridian-by-formula.html

Sunday, June 5, 2016

Sextant Lanyard




A sail tie makes for a comfortable sextant lanyard when worn Robinhood style. This frees up both hands for the sailor while keeping the sextant securely close to the vest. Loop the sail tie through the sextant handle then figure eight the ends together.

Sunday, January 17, 2016

Latitude by Polaris

Sum the Q correction with the corrected sextant altitude (Ho) of Polaris to quickly determine north latitude.