Emergency Celestial NavigationNOTICE: 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. Timekeeping
Almanac Data
Prerequisite for Celestial Navigation is the availability of some basic almanac data.
For the Sun and stars, it is possible to compile compact longterm (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 "fullyfeatured" Nautical Almanac is required. Graphical Method for Sight Reduction
Without appropriate SightReduction Tables and electronic calculator it is still
possible to obtain a result for the SightReduction 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 ReductionRecently, 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/NewcompactbackupCELNAVsystemchangedforarchiveLaPookfeb2009g7414
The original usermanual for the Bygrave slide rule:
http://fer3.com/arc/m2.aspx/NewcompactbackupCELNAVsystemLaPookfeb2009g7419
Later Mr Robin Stuart posted his nice PostScript files for flat scales printing:
http://fer3.com/arc/m2.aspx/PostscriptcodeformakingBygraveScalesStuartjan2015g29918
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,
Tony
More details can be found on the following page (under construction):
Bygrave method for Sight Reduction

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