A GREAT WORK

Hokitika Guardian, 3 December 1929, Page 3

A GREAT WORK

THE NAUTICAL ALMANAC

The Nautical Almanac and Astronomical Ephemeris for the year 1931 has been issued by the British Admiralty. After being -published iir the same form for ninety-seven years, the ar-„, rangement of the Almanac has been radically changed, and brought thoroughly up-to-date so as to be of the greatest service not only to navigators and "observers, but also to the army, of computers where work extends into the domains of dynamical astronomy as ..well as those of spherical astrpriomy,,. We might note here that these vastimprovements . are in the main due to the Deputy-Superintendent, Dr. L. J. Comrie, who is a New Zealander. In' congratulating him oil his splendid achievement, New Zealanders are proud of the distinguished reputation which their countryman has establish ed.

A sketch of the history of the British' Admiralty Nautical Almanac should prove interesting to the lay as well as to the astronomical- reader. The x\lmanac, of course, owes its existence to the fact that navigators must have a means of determining the positions of their ships at sea. To the same fact, the Royal Observatory of Greenwich owes its foundation. To determine the position of a ship at sea, it is necessary to know the Greenwich Mean Time, the altitude (or angular distance above the horizon) of some heavenly body, and the position (Right Ascension and Declination) in the sky of that body. To-day the Greenwich mean time is supplied by a reliable chronometer checked several times a day by radio time signals transmitted from various parts of the world; the altitude is found by a careful observation made with a sextant, and the position of the heavenly body is interpolated out of the tables given in the Nautical Almanac. With these data, the position of the ship can be obtained to within a minute of arc after a few minutes’ calculation by, say, the “ Sumner ” or the Marcq St Hilaire” method of reduction.

Three centuries ago, however, it was quite another matter, and it was with the aim of assisting the navigator that the Royal Observatory was established, and the first Astronomer Royal—the Rev John Flamstead—appointed in 1(576 by Charles 11. to “apply all his care and activity to correcting the tables of celestial movements and the positions of the fixed stars to the end of providing means for the determination off longitude for perfecting the art of navigation.” It certainly was time for something to be. done, since up till well into the eighteenth century, using the best tables existing—those by Mayer, of Gottingen—it required several hours to compute a position to within one degree! The Nautical Almanac giving the positions and movements of the heavenly bodies, of course, followed as a natural corollary to the Royal Observatory, and made its'first appearance in 1766 under the editorship of the Rev Nevil Maskelyne, then Astronomer Royal. The publication, however, soon became the object of international Tiilicufe'owing to the notorious terrors which appeared in it; for ex-

ample, the omission of the 29t1; of-Feb-ruary one leap year. ! About 1819, the Royal Astronomical •Society was invited by the Admiralty to reform the Nautical Almanac, an opportunity which was at once seized upon. The society demanded a complete reformation down to the most minute detail, even having included the date, of the. beginning of the Moliam- j medan fast to Ramadan, which was considered as being of possible value to j navigators in tbe neighbourhood of , Molvafnmedan States. All the. demands of the Royal Astronomical were agreed to, and in 1834-appeared the first Nautical Almanac.of the new .type,. arranged in the manner which has been preserved up to the 1930 Alrhariae, but which has again been( drastically re-, formed by Dr Cpmrie in the 1931 edition. . . I

The Nautical Almanac ' and Astronomical Ephemeris is composed of something like seven hundred pages of tabulated figures'giving the daily positions, or ephemerides, of the sun, moon, planets, satellites of the planets, and about five hundred stars. There is much other information also, such as the data required for eclipses and

occultations, sunrise and sunset, moonrise and moonset, on. In all, somewhat over a million figures are printed on its pages. Of course, there is much that has no direct interest for the navigator, so a separate volume is also issued giving only such data as are necessary-at "ffea. ■

Naturally, most important countries publish their own Almanacs, since the directions and .explanations given must be in n language with which the navigator is familiar. .For example, France issues the “ Connaisance des Temps,” which is prepared by the Bureau des Longitudes at Paris. Germany issues the “Berliner Astronomisches Jahrbuch,” which is prepared by the Astronomisclien Rechen-lnstitut in Berlin; and the United States of America

issues the “ American Eplvemeris and Nautical Almanac,” prepared by the United States Naval Observatory. All these publications have, up till now, been very similar in arrangement and variety of data, but exhaustive comparison shows clearly that the 1031 British Admiralty Nautical Almanac is of a much higher standard than any other.

Although there are so many almanacs published, the labour of computation has since 1896 been divided. For example, positions of the sun and moon are calculated in England, eclipses are calculated at Washington, certain star places are computed at Paris, others at Berlin, and so. on. In this way an enormous amount of duplication of very arduous computing work is avoided.

The Nautical Almanac is always published several years ahead for the convenience of those who have to predict in advance such phenomena as tides, etc. Thus the 1931 Almanac was issued this year, the 1932 number is in the press, and some of the computations in volved in the preparation of the publication are as far advanced as the year 1940. The 1931 edition of the Nautical Almanac contains so many marked reforms and improvements that its appearance marks an important epoch in the history of the publication, and will be ever a monument to the indefati-

gable genius of Dr Comrie, Deputy-

Superintendent of his Majesty’s Nautical Almanac Office, who has, by the introduction of these many and varied ek-nirrps. earned the gratitude and praise of the astronomical world.

and undertaken with all cheerfulness. A gift, has come clown from the past. Let it he preserved for the present, that its jovs may be passed on to the future for the pleasure and interest of those who came after.