NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Better/easier GHA(Aries) formula?
From: Gary LaPook
Date: 2018 Jul 17, 23:47 -0700
From: Gary LaPook
Date: 2018 Jul 17, 23:47 -0700
Re: 3-Star Fix - "Canned Survival Problem"
From: Gary LaPook
Date: 2008 Jun 14, 03:44 -0400
Being the conscientious navigator that I am, I followed my usual practice of memorizing some data from the 2008 Nautical Almanac so that I would have it available for emergency use.
The first thing I memorized was the GHA of Aires at 0000 Z January 1, 2008 which is 100º 01.9' and also remembering that Aires advances 59.139' each day. With this information you can calculate GHA Aires for 0000 Z on June 9, 2008 which is the 161st day of the year but is only 160 days from January 1st. So multiplying 59.139' times 160 days gives 157º 42.2' to which you add the starting value of 100º 01.9' to come up with the GHA Aires on June 9th at 0000 Z of 257º 44.1'. To this you add the change of GHA for the time since 0000 Z (3 hours 42 minutes 10 seconds for the Vega shot) by multiplying the time interval by the rate of change of 15.041º per hour making 55º 41.6' making the GHA Aires at the time of the Vega shot of 313 º 25.7'.
The first thing I memorized was the GHA of Aires at 0000 Z January 1, 2008 which is 100º 01.9' and also remembering that Aires advances 59.139' each day. With this information you can calculate GHA Aires for 0000 Z on June 9, 2008 which is the 161st day of the year but is only 160 days from January 1st. So multiplying 59.139' times 160 days gives 157º 42.2' to which you add the starting value of 100º 01.9' to come up with the GHA Aires on June 9th at 0000 Z of 257º 44.1'. To this you add the change of GHA for the time since 0000 Z (3 hours 42 minutes 10 seconds for the Vega shot) by multiplying the time interval by the rate of change of 15.041º per hour making 55º 41.6' making the GHA Aires at the time of the Vega shot of 313 º 25.7'.
I made one change in my procedure and you might like to do the same. Instead of memorizing the GHA of Aries for 0000Z on January 1st I memorize it for December 31st of the prior year. This way the number of days that you have to multiply the daily change in the GHA of Aries is simply the number of the day in the year while if using January 1st you must subtract "1" from the number of days in the year. For example, January 31st is the 31st day of the year yet only 30 days have elapsed since January 1st but it is 31 days since December 31st.
http://fer3.com/arc/m2.aspx/3Star-Fix-Canned-Survival-Problem-LaPook-mar-2012-g18346
