NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Ho 249
From: Jeremy C
Date: 2011 Jan 16, 07:06 EST
From: Jeremy C
Date: 2011 Jan 16, 07:06 EST
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@pacbell.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@vwc.edu> wrote:
From: Patrick Goold <goold@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@pacbell.net> wrote:
"I am still unclear how to read the reduction tables. Thanks so much!"
Which tables are you using?
gl
----------------------------------------------------------------
NavList message boards and member settings: www.fer3.com/NavList
Members may optionally receive posts by email.
To cancel email delivery, send a message to NoMail[at]fer3.com
----------------------------------------------------------------
--
Dr. Patrick Goold
Department of Philosophy
Virginia Wesleyan College
Norfolk, VA 23502
757 455 3357
Charles Olson: "Love the World -- and stay inside it."