A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: What do "d" and "v" really stand for?
From: Gary LaPook
Date: 2008 Jun 19, 22:41 -0700
From: Gary LaPook
Date: 2008 Jun 19, 22:41 -0700
Except that there are no "v" or "d" corrections with the Air Almanac since the period between tabulated data is only ten minutes and, to the accuracy of that almanac and in flight CN, there is no loss by ignoring such slight changes for such a short interpolation period. gl On Jun 19, 11:52 pm, "Greg R."
wrote: > --- glap...@pacbell.net wrote: > > "v, the difference between the actual change in GHA in one hour and a > > constant value used in the interpolation tables; and d, the change in > > declination in one hour." > > Right, those tell what "v" and "d" are (and like I think anyone who's > reduced sights manually would know what they are) - but my original > question was what actual words the letters are abbreviations for. > > BTW, I originally learned celnav with the Air Almanac (way back in the > mid-70s - at the time it looked "easier" than using the Nautical > version), but I'd be totally lost if I had to use it now... ;-) > > -- > GregR > > --- glap...@pacbell.net wrote: > > > Look at article 1903 in Bowditch, available here: > > http://www.nga.mil/MSISiteContent/StaticFiles/NAV_PUBS/APN/Chapt-19.pdf > > > > > "v, the difference between the actual change in GHA in one hour and a > > constant value used in the interpolation tables; and d, the change in > > declination in one hour." > > > gl > > > On Jun 19, 10:41 pm, glap...@pacbell.net wrote: > > > Here are excerpts from the 1937 N.A The first page shows the time > > of > > > transit of the moon of the Greenwich meridian and contains a "Var. > > per > > > hour" column, variation?, the change in declination inone hour." > > > >http://www.geocities.com/fredienoonan/almanac-1937-136.JPG > > > > The second page contains moon data showing GHA and DEC and has > > > separate increments tables for each day based on the the dec change > > > and GHA change rates for that particular day. no "v" or "d" > > correction > > > factors are shown. > > > >http://www.geocities.com/fredienoonan/almanac.html > > > > This third link takes you to a site I put up with with excerpts of > > > various navigation texts. > > > >http://www.geocities.com/fredienoonan/ > > > > gl > > > > On Jun 19, 9:00 pm, frankr...@HistoricalAtlas.net wrote: > > > > > Greg, you asked: > > > > "And maybe that's going to be about as good an answer as we can > > hope for > > > > at this point in time - does anyone know when "d" and "v" terms > > first > > > > showed up in the NA as such? There might be more elaboration > > about what > > > > the abbreviations stood for when they were first introduced." > > > > > Yes, that's basically what I was providing you in the previous > > message. The > > > > labels "v" and "d" first appear in the "Abridged Nautical > > Almanac" in 1952. > > > > This is the earliest date when the official British almanac > > included GHA. > > > > This had been introduced 18 years earlier in the American > > Nautical Almanac, > > > > and it was also widely used in the various air almanacs. As I > > said, the > > > > concept of the interpolation constant at the foot of each column > > on the > > > > almanac page was already present in the American almanac where it > > was called > > > > a "code". I also checked a couple of commercial British almanacs > > from this > > > > period (the commercial British almanacs adopted GHA well before > > the official > > > > British almanac). They use a similar principle but again not > > labeled v and > > > > d. So my best guess right now is that the first use of these > > specific labels > > > > for the interpolation data is the British "Abridged Nautical > > Almanac" in > > > > 1952. Here's the full text from the explanation in the AbNA for > > 1953: > > > > "Interpolation between the tabulated hourly values is provided > > for by > > > > comprehensive interpolation tables, printed on coloured pages at > > the end of > > > > the book, giving for every minute and every second the increments > > of G.H.A. > > > > corresponding to the mean rate of increase for the Sun (15� > > precisely), the > > > > constant rate for Aries (15� 02'.46) and the minimum rate for the > > Moon (14� > > > > 19'.0). The variations from the means are so small for the Sun > > that they > > > > have been deliberately ignored; the tabulated hourly values of > > the Sun's > > > > G.H.A. have been adjusted so that the error thus caused is a > > minimum. These > > > > variations cannot be ignored for the planets or for the Moon, and > > > > corrections have to be made for the excess (v) in hourly motion > > over that > > > > adopted in the main interpolation tables." > > > > > So there's an answer: v stands for "excess". :-) > > > > > In the next paragraph: > > > > "The corrections for these VARIATIONS [...] are taken directly > > from the > > > > interpolation tables with argument v" and "A similar procedure is > > used to > > > > interpolate the declinations of the Sun, Moon and planets; here > > d, the > > > > hourly DIFFERENCE, is given without sign on the daily pages" (I > > have > > > > capitalized those two words for emphasis). So if you must assign > > a meaning > > > > to v and d, I think the best bets are "variation" (of the rate of > > change of > > > > GHA from the selected mean rate) and "difference," but the catch > > is that the > > > > person who wrote this explanatory section may very well have > > invented those > > > > origins on the spot. > > > > > By 1958, when the modern Nautical Almanac was formed by the > > merger of the > > > > American Nautical Almanac and the Abridged Nautical Almanac (they > > kept their > > > > separate names until 1960), the explanation simply refers to v > > and d values > > > > with no hint of any etymology. Same in Bowditch of the same era. > > I think > > > > this is intentional. The labels v and d really are not intended > > to "stand > > > > for" anything. > > > > > -FER --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To unsubscribe, email NavListemail@example.com -~----------~----~----~----~------~----~------~--~---