A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: David Pike
Date: 2021 Jun 2, 07:28 -0700
If you’re intending to use HO249, you might like to consider using the Air Almanac rather than the Nautical Almanac. It’s simpler and gives GHA for every ten minutes, but it still gives you an accuracy compatible with HO249. Also, both are available free online. Unfortunately, although I downloaded the 2021 AA recently, I can’t now find the link. It doesn't want to file transfer either. Then I’d build up slowly starting as if I was aiming at the Sun’s centre, (HO249 Vols 2 or 3). You do that all the time with an aircraft sextant. Then I’d start adjusting for lower limb shots. I’d ignore the planets and Moon until I was more confident.
After that, I’d go on to stars, (HO249 Vol1). Make sure you’re using the correct epoch. You probably will be if you’ve just downloaded HO 249 online. I’d start with just single star position lines before going on to two-star sandwich fixes and three-star fixes and all the extra plotting refinements the three-star involves. Realistically, if you’re planning to eventually obtain your readings with a marine sextant, you should be practising with stars which are visible at twilight, so pick bright ones. Stellarium App on your smartphone is great for identifying them from planets as they come into view after sunset, especially if your phone has a magnetometer.
While Mary Blewitt is excellent; Tom Cunliffe’s Celestial Navigation, which is available second hand on Abe Books for a couple of £s (https://www.abebooks.com/servlet/SearchResults?an=Cunliffe&tn=Celestial+Navigation), follows much the same path, but there’re many more coloured diagrams and photographs and it also gives a few worked examples.
Overall though, I think Frank’s is a great idea. DaveP