Emergency Celestial Navigation
NOTICE: this page is under construction and currently only
a draft with a collection of ideas to be elaborated!
Increasing reliance on complex electronic navigation systems - nowadays generally
available on pleasure yachts - has changed the perspective of emergency navigation.
Today, it is more likely that a navigator will suffer failure of electronic devices
or the associated power supply and be left with little more than a sextant to
navigate with, than that he will be forced to navigate a lifeboat.
Prerequisite for Celestial Navigation is the availability of some basic almanac data.
For the Sun and stars, it is possible to compile compact long-term (10 years and more)
almanac data which are accurate enough to make them suitable for rough navigation.
An appropriate version of such an almanac can easily be kept in the sextant box.
The apparent motion of the Moon and the Planets on the other hand are not regular
enough to achieve such compact almanacs.
For these celestial objects a "fully-featured" Nautical Almanac is required.
Graphical Method for Sight Reduction
Without appropriate Sight-Reduction Tables and electronic calculator it is still
possible to obtain a result for the Sight-Reduction calculation with the following graphical method.
I have to credit Marco A. Costa, for the insight that there is a simple
method of graphically multiplying Sine and Cosine values.
Bygrave Slide Ruler for Sight Reduction
Recently, I received a mail from Tony, who pointed me to a very interesting option for emergency navigation:
Dear Erik, In my study of the availale sight reduction options I learned about the Bygrave slide rule. http://fer3.com/arc/m2.aspx/New-compact-backup-CELNAV-system-changed-for-archive-LaPook-feb-2009-g7414 The original user-manual for the Bygrave slide rule: http://fer3.com/arc/m2.aspx/New-compact-backup-CELNAV-system-LaPook-feb-2009-g7419 Later Mr Robin Stuart posted his nice PostScript files for flat scales printing: http://fer3.com/arc/m2.aspx/Postscript-code-for-making-Bygrave-Scales-Stuart-jan-2015-g29918 With just 3 (three) slide rule operations and very little arithmetics in between - one obtains a LoP and intercept without having to have Ageton's or any other bulky SR tables. I'm very much impressed! Warmest regards, TonyMore details can be found on the following page (under construction): Bygrave method for Sight Reduction
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