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Improvement in Star Finding
(See page 79, January, 1942, Proceedings)
Commander K. J. Christoph, U. S. Navy.—This is a small-size star finder consisting essentially of a transparent, micalike template 8 inches square, used with Paper horizon plates, also 8 inches square. The principal navigational stars are plotted on the template, with right ascensions as abscissas and declinations as ordinates. The right ascension abscissas serve also to indicate L.C.T.’s. There are 6 horizon plates, together covering latitudes °f 0° to 50°, North or South. Each plate has a series of altitude and azimuth curves, and is graduated horizontally at the top into calendar months and days.
The device is operated by choosing the aPpropriate horizon plate (corresponding to the observer’s approximate latitude), placing it underneath the template, and adjusting the two horizontally and vertically so that the L.C.T. and declination on the template match the date and latitude, respectively, on the horizon plate. The star’s approximate altitudes and azimuths may then be read from the curves on the horizon plate.
From the foregoing, it will be seen that this star finder is similar to Rude’s in Principle and operation. The difference between them lies in their construction— specifically, Brownell’s shows the celestial sphere as square-shaped, while Rude’s shows it as circular.
This star finder is neat in construction and accurate in results. Its small size, flexibility, and very light weight commend it where economy of space is important, as in aircraft. Paradoxically, its commending small size is a condemning fault. The printing and graduations, comparatively fine because of the smallness of the device, are not easy to read. They are particularly trying on the eyes and patience when making the required two-way adjustment of the star template superimposed on the horizon sheet. Another fault is that, with a single adjustment of the template and sheet, the star finder will not encompass all visible sky, except for certain times of the year. Many stars are thus found to be outside the limits of the altitude and azimuth curves; and to bring them in, a second adjustment is required.
The German Air Almanac
(See page 1594, November, 1941, Proceedings)
Captain Radler de Aquino, Brazilian Navy.—Mr. E. B. Collins’ article was timely, as this year has seen the rebirth of the American Air Almanac under a new and the most convenient form and the completion of that colossal undertaking H. O. Publication No. 214 where altitudes and azimuths are tabulated for latitudes 0° to 79° and for the necessary hour angles and declinations in 8 large volumes containing over 2,000 pages.
Mr. Collins indicates that “the American Air Almanac is almost an exact replica of the British edition.” However, the single entry in the American Air Almanac has a slight advantage over the double entry of the British Air Almanac. Besides the American Air Almanac gives the planets for every 10m, while the British gives them for every hour.
Mr. Collins gives his American readers a glimpse of the German Air Almanac based upon the use of a sea and air chronometer graduated in degrees and minutes of arc, as arguments. Attention is called to an article by the writer in the Naval Institute Proceedings for October, 1937, entitled “Sidereal or Mean Time Chronometers?”
Mr. Collins shows how the Germans succeeded in reducing the size of their Air Almanac to one half of the others by means of the sea and air chronometer, as the writer already indicated it would in the above article on page 1432. However, to further simplify the finding of the G.H.A. of 16 stars, the German Air Almanac tabulates them on one daily page, thereby doubling unnecessarily this publication just for these 16 stars, and having to rely on the usual method of combining the G.S.T. in arc, or G.H.A. T as it is called now, with the versed ascension (shortened to versascension by Mr. Collins) for the rest of the navigational stars.
The writer has shown that in the case of all stars a sea and air chronometer regulated to sidereal time in arc would avoid the need of tabulating the G.H.A. of the navigational stars and would offer the simplest and easiest way of finding their G.H.A.
The bugbear of converting mean time into sidereal time to regulate this chronometer has disappeared now that the American Air Almanac and British Air Almanac give the G.S.T. in arc or G.H.A. T for every 10“ of G.C.T. or G.M.T. as the British call it.
This means that these air almanacs could be reduced to one-sixth by giving the data required for every hour instead of every 10“, provided the moon was tabulated separately.
In comparing the American and the British with the German Air Almanac, copies of which I received in 1939 from Captain Kunze, Chief of the Nautical Division of the Oberkommando of the German Navy, for the last two trimesters of 1939, one can see there is no advantage for the sun and the planets and only a slight gain for the stars in view of the smaller corrections, but this requires a daily page tabulating only 16 stars.
The writer cannot see any advantage in giving G.H.A. from the lower branch of the Greenwich meridian and Mr. Collins’ examples show that to obtain L.H.A. from the upper meridian you have either to subtract 180° from the result or add 180° to obtain the L.H.A. west.
Mr. Collins informs us that “the German aviator uses a navigation watch reading to degrees, minutes, and tenths of a minute of arc.” The figure he shows is one of Longine’s sea and air chronometers of 1939, as manufactured by them with the technical assistance of the writer, who claims he was the first to suggest their use to Captain J. F. Hellweg, U. S. Navy, then and now Superintendent of the U. S. Naval Observatory, on July 5, 1933, after he had seen and used in the air the first American Air Almanac for the year 1933.
It is hard to say during these trying times if the sea and air chronometer graduated in degrees and minutes of arc will find favor with the great majority of sea and air navigators all over the world, but its principal advantage is that it gives them immediately without any calculation whatsoever just what they require, viz.: G.H.A. of the sun when regulated for G.A.T. in arc less 180° and G.S.T. in arc or G.H.A. T for the time of the observation.
Examples given in H. O. No. 214 and
H. 0. No. 216 show that there is quite a need for reducing further the calculations involved in the determination of L.H.A. in arc and the sea and air chronometers are the best answer to these simplifications. Considering G.H.A. and L.H.A. always west from 0° to 360° would further reduce the calculations and would avoid the need to draw a time and longitude diagram for determining the local hour angle. For those tables like H. 0. No. 211, 208, and 214 and many others, where no provision Js made for a direct entry with L.H.A. west from 0° to 360°, a reduction to 180° E. or W. has to be made.
The fact that the sea and air chronometer saves the trouble of converting time into arc is not all. It cuts out the chronometer correction and the equation of time and permits also the correction of the daily rate of the chronograph (rattrapant) pointers, one of which keeps the exact tenth of a minute of arc, and the other acting as a stop watch makes the observer independent of an assistant.
The writer was pleased to notice that the tabulation of G.H.A. for the stars contained in the American Nautical Almanac was dropped in favor of the combination of G.H.A. T with the versed ascension or S.H.A. in the new American Air Almanac.
Commander Sinton’s remarks on Mr. Collins’ article seem to be in accord with the late Admiral Newton’s remarks that “any simplification of value in air navigation is equally convenient and useful in sea navigation” (Naval Institute Proceedings for October, 1937, page 1432).
Anyone interested in the historical development of these air almanacs should read a “Discussion on the Air Almanac,” published in the Geographical Journal for August, 1938, issued by the Royal Geographical Society, London. It indicates the situation just before the final adoption of the new form of the British Air Almanac for January, 1939, and gives a glimpse of the new Astronomical Navigation Tables prepared by H. M. Nautical Almanac Office on behalf of the Air Ministry.
The U. S. Navy Department, the U. S. Hydrographic Office, and the U. S. Naval Observatory deserve all credit for giving the world such far-reaching and useful publications as H. O. No. 214 and the new American Air Almanac for the year 1941.