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    Re: Ho 249
    From: Gary LaPook
    Date: 2011 Jan 16, 13:14 -0800
    Interesting points you bring up.

    Volume 2 & 3 can be used all the way up to 29° 59' since you always interpolate upward. There is only one star, of the 57, that has a declination in this range, Fomalhaut.

    H.O. 249 was first published in 1951 and was intended for air navigation, particularly for the use of navigators on American bombers on their way to Russia. Since, by that time, these planes flew in the stratosphere (as in B-47, Stratojet, which also entered service in 1951, and the B-36 was up there too) they flew above the clouds so the 7 stars listed in Volume 1 were unlikely to be blocked by clouds so were sufficient. Volume 1 is very convenient for flight navigators since they normally use only one AP based on the GHA of Aries for all three shots.They can do this because the normal shooting schedule is to shoot stars exactly four minutes apart so the GHA of Aries will have changed by one degree so the minutes of GHA Aries will be the same for each shot allowing the use of one AP. The LOPs are advanced mathematically by adjusting Hc and usually the one degree change in GHA Aries is also dealt with mathematically by adjusting the Hc, all of which allows for the use of one AP for plotting all three LOPs. I'm quite partial to volume 1.

    See:

    https://sites.google.com/site/fredienoonan/other-flight-navigation-information/working-the-sight-in-flight

    and

    https://sites.google.com/site/fredienoonan/other-flight-navigation-information/in-flight-celestial-navigation

    Volume 1 uses 41 of the 57 listed stars including 17 whose declinations exceed 30 degrees. Looking at latitudes 34 north and 34 south, for example, every group has at least one high declination star and almost all have 2 or 3 such stars. This was a follow on to H.O. 218, published during WW2, which only used 22 stars. Of the 57 listed stars, 30 are usable with volume 2 & 3 so only 10 northern stars and 17 southern stars aren't. So if the star you want to shoot isn't in volume 1 there is a very good chance that it can be reduced with volume 2 or 3. Also, the Nautical Almanac actually has data for 173 stars so an additional 30 stars having declinations less than 30 degrees, making 60 in total, can be reduced with volumes 2 & 3.

    Last year, on the 437 foot Royal Clipper,  I found that the only sight reduction table carried was H.O. 249 so, it appears, that even on some large ship, navigators find it sufficient for their navigation.

    gl

    --- On Sun, 1/16/11, Anabasis75---.com <Anabasis75---.com> wrote:

    From: Anabasis75---.com <Anabasis75---.com>
    Subject: [NavList] HO 249
    To: NavList@fer3.com
    Date: Sunday, January 16, 2011, 4:06 AM

    There is a big difference between HO 249 and HO 214 or HO 229, and that is the limited declination range of Volume 2 and 3, and very limited number of stars available in Volume 1.
     
    As I see it, HO 249 intends the navigator to use Volume 2 or 3 (depending on Latitude) for your sun, moon, and planet sights and then use Volume 1 (selected Stars) for any star observations.  The main reason that the volumes are smaller is that they have only 29 degrees of declination included instead of the full 90 degrees.  Sadly this limitation eliminates 28 of the main navigational stars, many of which are nice to use in the lower to mid-latitudes, unless they are included in the pre-determined selected stars for your latitude and LHA of Aries in Volume 1.
     
    Of course in this day in age with the computers and calculators this isn't much of an issue, but if you like your tables and see a star poking through the clouds and it's outside of the range of HO 249, you are out of luck.  This won't happen with HO 229 since it's good for the full range of celestial triangles.
     
    HO 229 can also be used for great circle sailings and star identification.  HO 249 can do GC sailings as well, but only if you aren't sailing above 29 degrees of Latitude.  Star ID is also limited by declination.
     
    In the end you are trading weight and bulk for versatility and accuracy, and people should understand this when they choose what book to use.
     
    Jeremy
     
    In a message dated 1/16/2011 6:43:58 A.M. Central Asia Standard Time, glapook---.net writes:
    H.O. 229 takes up a lot of space and is heavy and provides more precision than is actually needed for small craft navigation. H.O. 249, Sight Reduction Tables for Air Navigation,  is much more compact and the arrangement of the tables is more convenient. Both tables are used the same way (with the exception of the second differences correction for slightly greater accuracy for high altitude sights in H.O. 229 that you can skip if you choose) so if you can work one set of tables you can work the other. I suggest you download H.O. 249 from this site:


    http://msi.nga.mil/NGAPortal/MSI.portal

    (click on "Publications")

    print out a few pages and compare with your H.O. 229.

    You can check your work by having the Navy do the computations here:

    http://www.usno.navy.mil/USNO/astronomical-applications/data-services/cel-nav-data

    Since you are just getting started, and before you head gets polluted with these other complicated methods, I suggest you try the flat Bygrave slide rule which you can make for yourself at a cost of a few dollars with the printouts available here:

    https://sites.google.com/site/fredienoonan/other-flight-navigation-information/modern-bygrave-slide-rule

    https://sites.google.com/site/fredienoonan/other-flight-navigation-information/self-contained-long-term-celestial-navigation-system

    The Bygrave computes everything your need in less than two minutes and uses no batteries.

    gl

    --- On Sat, 1/15/11, Patrick Goold <goold{at}vwc.edu> wrote:

    From: Patrick Goold <goold{at}vwc.edu>
    Subject: [NavList] Re: help with sun sights
    To: NavList@fer3.com
    Date: Saturday, January 15, 2011, 2:15 PM

    Gary,
    I am using HO 229. 

    Patrick


    On Fri, Jan 14, 2011 at 10:22 PM, Gary LaPook <glapook---.net> wrote:

    "I am still unclear how to read the reduction tables. Thanks so much!"

    Which tables are you using?

    gl
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    --
    Dr. Patrick Goold
    Department of Philosophy
    Virginia Wesleyan College
    Norfolk, VA 23502
    757 455 3357

    Charles Olson: "Love the World -- and stay inside it."

       
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