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    Re: Learning celestial navigation
    From: Robert VanderPol II
    Date: 2017 Mar 17, 13:25 -0700


    Where are you?  I'm looking to start a CelNav class at my Yacht Club in San Diego.

    You've got a really good start on cheap with the Davis-3.  4 or 5 cheap water proof digital watches from Amazon would be next.  A steel Ammo box from Costco after that. Then you come to sight reduction methods and almanac.

    To me the easiest sight reduction method is a Brown-Nassau but there are availability issues so bad you would need to make your own.  Cheap and certainly doable but not easy by any stretch of the imagination.  Your best bet is Publication-249, cheap ($18 for my 2 volumes), easy and fast.  It was designed to be used by aircraft during WW-II so fast, small (2-8.5x11 vol) and easy were prized over ultimate accuracy.  On a recreational boat at sea the results you can consistently get from even a high end metal sextant are not as good as the sight reduction in Pub-249 so you won't be loosing much by using 249.  If you need to go high latitude that changes but 249 is the place to start.  You can get a PDF free from the US gubmint at http://msi.nga.mil/NGAPortal/MSI.portal?_nfpb=true&_pageLabel=msi_portal_page_62&pubCode=0012

    There are a number of ways to go for an almanac (it tells you where in the sky a celestial body is at any moment).

    1]  The Nuatical Almanac is the default choice.  1 volume, all normal navigational star plus a few, moon and planets.  $25/yr or so, 368 pages.  Barnes&Noble has 2017 for $17 for the current year.  Included is a copy of Davey's sight reduction tables (aka NASR: Nautical Almanac Sight Reduction) which are on the order of 60 pages but they're a pain to use.  This almanac is what I will use to teach, thoug I may only have 1 or 2 copies and print daily pages from another source for class days.

    2]  You can get any number of apps that will preprint any number of pages of the full almanac will all normal celestial bodies out at least several years.  Some apps are free but the printing becomes a chore for emergency use and if you didn't pre-print the days you need you are SOL.  An app is probably the way to go for learning in the short term, but really you want to use and become comfortable with whatever paper almanac you decide to carry with you.

    3]  There is a long term almanac in Pub-249 that expired in 2016 that was good for sun and stars.  I would be comfortable looking at the progression of the annual correction table and forcasting my own correction table.  That would be good for 5yr or so more but I wouldn't trust it past 2027.  It may be that another long term almanac will be issued in the next edition of Pub-249.  FREE, 8-10pages.

    4]  GKolbe created a long term almanac good to 2050, accurate for the sun and stars to 0.1 arc-min for most of that period. In the back there is a copy of Davies sight reduction tables.   $35, 111pg including Davies and all or almost all the ancillary tables you need.   The almanac is reasonably easy to use, however it does involve a multiplication step for every body and may involve subtraction steps for some stars.which decreases ease of use.  This is what I am using currently when I play with CelNav away from home.

    5]  I am creating a long term almanac.  It will be good to 2035, for sun, stars, maybe the moon and maybe the planets.  Accuracy will be around 1arc-min so the same as Pub-249.  This is at least a year out and who knows, maybe never I could fall of the boat and drown tomorrow,  just kidding the boat has been sitting on the front lawn pissing off the neighbor for over a year but the club may find a spot for me to keep in the next 2 month.  I'm hopeful but not holding my breath.  I'll proably release the sun and stars in the next 6mo or so to see how people like it and get feed back.  Bug me at the end of 2017.

    The reason for the ammo box is to protect the watches.  The most likely reason to loose all your electronics including digital watches is a lightning strike.  I would put the patches and my spare HH-GPS, a solar charger and some Ni-MH batteries of the appropriate size in the ammo box which has a reasonable change of protecting them all from a strike.  The reason to have multiple watches is to average all the time from the watches and to know if any one has started to behave erratically.  Once you getting going on the CelNav let us know and somebody can explain the ins and outs of maintaining accurate time.  

    The ultimate in backup timekeeping is a mechanical watch which is less likely to be affected by a lightning strike unless there is some induced magnetism.  I have a $35 Soviet pocket watch that I have not yet checked the rate on.  I know a site you can get one for about $150 that has been serviced and possibly had the error rate checked.  Servicing is the hard part, checking error rate is something you can do.  There are more recent mechanical watches but they are all fabulously expensive or are automatic, that is self-winding when you wear them and I don't know how consistent the error rate is with an automatic.  More for me to research.

    Good luck.  If you are close I could help in person.

    Bob II

    Learning celestial navigation
    From: Tom Regan
    Date: 2017 Mar 16, 16:08 -0700

    In your opinion, what is the quickest, easiest and least expensive way to learn celestial navigation.  I just purchased a Davis Mark 3 and would like to learn the basics as a backup for electronic marine navigation.


    Tom Regan

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