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@aol.com <Anabasis75@aol.com> wrote:
From: Anabasis75@aol.com <Anabasis75@aol.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@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
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---------------------------------------------------------------- -- Dr. Patrick Goold Department of
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