It's hard to argue that astro navigation is essential. You could buy a perfectly good GPS set for the money you might spend on astro reference books alone, and several back-ups for the price of a decent sextant.
But there is something enormously satisfying about handling a sextant, and using a piece of Georgian technology for its intended purpose. And there's a kind of freemasonry about astro: a sense that until you've been initiated into its secrets and mysteries, you're not quite a proper Navigator.
The funny thing is that although a lot of astro jargon has an almost mystical ring about it, most of us already know the "secrets" on which the whole science of astro navigation is based.
2. All Done By Mirrors - The Sextant
3. The Celestial Sphere
5. The Noon Sight
6.Morning and Afternoon Sun Sights
8. Morning and Evening Stars
10. The Moon
Appendix 1 - Plotting Sheets