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Navigational Almanacs for small Computers and Calculators
Published online by Cambridge University Press: 23 November 2009
Extract
In 1947 Dr G. M. Clemence, then Director of the Nautical Almanac Office at the US Naval Observatory, and I visited a number of US institutions engaged in the development of digital computing machines, with a view to their application to the calculation of astronomical ephemerides. We were, at that time, planning the revision of the almanacs for surface navigation which led, in due course, to the unification of The American Nautical Almanac and The Nautical Almanac, Abridged for the Use of Seamen in essentially its present form as (from 1960 onwards) The Nautical Almanac. We were told (actually by an astronomer, Dr T. E. Sterne) that our efforts were pointless since, in the near future, a navigator would be able to calculate the astronomical data that he required to reduce his observations by digital computer; conventional almanacs would no longer be needed. Thirty years later that optimistic forecast, although not yet realized, requires consideration. However, no one could have foreseen that the microprocessor of today is far more powerful than the most elaborate computer that was then practically visualized. For that matter, few would have thought that there would still have been a demand for astronomical data for navigation; the basic principles of many other aids to navigation were rapidly being developed.
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- Copyright © The Royal Institute of Navigation 1979
References
NOTES AND REFERENCES
1 The phrase ‘a precision of about’ is used here rather loosely, as the error distribution is often irregular with peaks at infrequent intervals, such as inferior conjunction for Venus. Full details are given in the publications referred to.Google Scholar
2 One use of such expansions in astronomy was introduced into the 1972 edition of The Astronomical Ephemeris for the geocentric distance of the Moon at intervals of 12 h. Some associated formulae are given in Interpolation and Allied Tables, prepared by HM Nautical Office (1974 edition, HMSO, 40p net).Google Scholar
3 See the National Physical Laboratory's Modern Computing Methods (HMSO, 1961) or any standard textbook on numerical analysis. These methods were used to provide the main astronomical data, for the Sun and stars, at monthly intervals in The Star Almanac for 1977; five terms, expanded as a power series, were used to represent R (for the stars) and E and Dec. for the Sun to a precision rather better than 1″. A. T. Sinclair gives a full description in Survey Review, 23 (1975), 178.Google Scholar
4Almanac for Computers for the year 1978, by Doggett, Le Roy E., Kaplan, George H. and Seidelmann, P. Kenneth, obtainable from the Nautical Almanac Office, US Naval Observatory, Washington, DC 20390, for $3 (payable to US Naval Observatory).Google Scholar
5 These series, developed by Van Flandern, T. C. and Pulkkinen, K. F. of the Nautical Almanac Office, were included in advance of full publication.Google Scholar
6 ‘NAO Technical Notes are produced primarily for internal circulation, and may contain information that is, for example, too preliminary or too detailed for formal publication. Although some will be given a limited external distribution, it is not intended that they should form a published series to which reference can be made in the literature.’ (Introductory note to the series.) However, it is intended that the material given in nos. 44, 46 and 47 will be consolidated in a Royal Greenwich Observatory Bulletin, which will be published for general use. Similar data for 1979 are given in RGO Astronomical Information Sheet No. 29.Google Scholar