NavList:

You wrote:
"The Nautical Almanac and the Air Almanac are both published by the USNO"

The Air Almanac would be a good example of government waste were it not so trivially cheap to produce. It is deadwood from an earlier era. I fear that some folks on NavList are under the impression that these almanacs are actually being "calculated" every year using the latest tools and analysis methods of positional astronomy. The positions of the Sun, Moon, and planets are KNOWN quantities for the foreseeable future, meaning centuries into the future, at the level of accuracy required by celestial navigation. There are no "theories" to consult. All that has to be done in any year is estimate the "watch error" of the Earth's rotation (that's this delta-T that everybody talks about) and then convert from one coordinate system to another (e.g. ecliptic latitude and longitude to GHA and Declination). These calculations are genuinely trivial. Because they are trivial, it is possible to continue the "Air Almanac" as an electronic resource at almost no cost. The work involved is probably fifteen minutes up to a few hours every year by one clerk working on a single computer somewhere out there in cyberspace. Then you spend a few hours sampling and comparing for basic quality control, and you're done. Upload to the server. That's all it means to "publish" the Air Almanac. So where's the catch? If it was near-perfect in 2001, why wouldn't it be near-perfect in 2011? The problems can range from operator error (maybe the clerk who took over this year doesn't know how to enter delta-T properly) to updates of underlying software products (like the software that generates output in pdf files --just as an example). With a marginal publication like this that has almost no practical value and an exceedingly small user base, entropy kicks in.

Also, I'm a bit puzzled by the concern over a single minute of arc difference in the Air Almanac. Isn't this by its nature a lower accuracy publication? Originally designed for air navigation, the precision is ten times lower than that of the Nautical Almanac. A minute of arc error is an unnecessary error, but it is also an inconsequential error for that publication. Nobody's going to use the Air Almanac for lunars!

As for the Nautical Almanac, it, too, is trivial to produce these days. Quite a few of us on NavList could produce an exact duplicate from scratch easily, and some of us have already produced functional equivalents. Since about 2005 I have made available an online nautical almanac which outputs the standard daily position data found in the printed almanac. It can be found here: www.HistoricalAtlas.com/lunars (scroll down to the third link). The official published Nautical Almanac is not produced by the USNO at all, though they do print their US edition with its distinctive orange cover. Rather, the Nautical Almanac is produced by a small semi-government operation in the UK, and by agreement, they supply their output to USNO for their edition. As noted above, they have very little work to do. The positional data is already known. It's a simple matter of updating delta-T (predicted value, of course) and making a few other small changes. Again, we're not talking about a staff of astronomers "compiling" the almanac. Picture instead a clerk updating a few entries once a year and clicking "generate pdf". Of course even a trivial process is not immune to operator error. One difference compared to the Air Almanac is that the Nautical Almanac is still widely disseminated and as a result the quality control is bound to be an order of magnitude better.

So why don't we publish our own Nautical Almanac? First, there's the clear value of the word "official". Ken Gebhart's "Commercial Nautical Almanac" benefits greatly from being able to state that it is an exact duplication, under license, of the data pages from the "official" Nautical Almanac. Second, the folks in the UK claim copyright to every aspect of the work that CAN be claimed under copyright. Don't worry: they can't copyright planet positions. That copyright claim includes most especially the layout of the pages but apparently also includes the list of 57 navigational stars (as numbered). Any of these claims are suspect and you could probably argue them in court if you have money to burn, but they have the economy of scale on their side. There are lawyers already on the payroll to pursue all such UK government copyright claims. So in the case of the data file that Andres posted which is an attempt to duplicate the layout of the official Nautical Almanac as nearly as possible, it is probably open to a copyright infringement lawsuit. Of course if the publisher stays under the radar, that's not going to happen. But then again, if we have to stay under the radar with these useful tools, what's the point? At some point, I suspect there will be a great proliferation of privately produced nautical almanacs (as electronic resources at least) and it will become impossible to defend the copyright claims. I doubt that the official Nautical Almanac, as a book published on paper, will even see its 60th anniversary in 2018, but I also expect that there will be a large number of privately-produced alternatives with many specialized to particular styles of navigation and particular interests and applications. There will be "nautical almanacs" supporting traditional celestial navigation but not "THE Nautical Almanac".

-FER

-FER

----------------------------------------------------------------
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
----------------------------------------------------------------