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Re: What do "d" and "v" really stand for?
From: Greg R_
Date: 2008 Jun 19, 21:52 -0700
From: Greg R_
Date: 2008 Jun 19, 21:52 -0700
--- glapook@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 --- glapook@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 , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---