A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Gary LaPook
Date: 2017 Jan 30, 15:27 -0800
Hi, Just studying Celestial Navigation. The book I have uses the Nautical Almanac and AP3270 for its examples. I mention this as I have become aware there are different methods/tables. I have just become aware of precession and nutation and realise all celestial navigation will have to take this into account, either by including it in the almanac or by the use of some other special tables. I am just curious to discover how precession and nutation is taken into account for all the heavenly bodies. Aries, Stars, Sun, Moon, Planets & Polaris. The only reference made to precession & nutation is for Polaris. I look forward to replies. Thanks Mike
Simple. If using the current Nautical Almanac or the current Air Almanac then the changes in SHA and declination caused by precession is reflected in those published coordinates. Look at the first and last days of the almanac and see the changes in these values. There is also a table near the back of the N.A. where these changing values are tabulated monthly. So if using HO 249 volumes 1 and 2 or HO 229 or HO 214 or HO 216 or HO 208 or HO 211 or other similar tables or a calculator then that is all there is to it. But if you are using HO 249 volume 1, the tabulated Hc's and Zn's are based on the postions of the stars in epoch 2010 for the government publication and epoch 2015 for the commercial edition available from Celestaire. Since the positions of the stars change during the ten year period that you use each edition of this book, there is a precession and nutation correction table included. Since the stars move in lockstep with each other, this correction is made to the final fix (the easy way) or to the assumed positions.