NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Ho 249
From: Gary LaPook
Date: 2011 Jan 16, 13:14 -0800
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@aol.com <Anabasis75@aol.com> wrote:
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