The Admiralty Manual of Navigation Vol 2: Astro Navigation

Satelite technology enables amlmost every mariner to use electronic navaids to fix thier position on the oceans.  However, electronic systems can be disrupted by errors in a satelite or its ground control systems, defects in shipboard equipment or interference with satelite signals.  The celestial chart therefore remains the most reliable tool for mariners navigating out of sight of land.  

This new edition of the classic guide to celestial navigation has been redesigned for clarity and contains guidance on using UKHO/Nautical Almanac Office's NavPac v4 software for astro navigation, including full colour screenshots.  With NavPac, a modicum of skill with a sextant and the appropriate chapter from the book, anyone can do astro.