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Published online by Cambridge University Press: 23 November 2009
In spite of, or perhaps because of, the almost universal use of some ftym of electronic calculator for the reduction of astronomical sights, there is a growing demand for a simple back-up method for emergency use when a calculator is not available. Presumably the need arises because of the disinclination to carry the material for a standard method in order to provide cover for the small chance of calculator failure. It is a surprising development, enhancing the continued interest in, and use of, astronomical navigation in a field increasingly dominated by instant and continuous position-fixing systems of high precision and universal applicability.
Similar considerations may apply to the ephemeris data, which are being increasingly generated by calculator or computer. However, to a precision adequate for emergency use, near-permanent data for the Sun and stars can be given in a few pages in tables similar to those for G.H. A. Aries (Vol. I) and the Sun (Vols. 2 and 3) in Table 4 of AP 3270 Sight Reduction Tablesfor Air Navigation. In fact the simplest conceptual solution might well be to carry the appropriate latitude pages extracted from the loose-leaf US edition, HO 249.
In 1948 I had occasion to review the existing tables for the reduction of astronomical sights (this Journal, Vol. 1, p. 298, 1948); the review was limited to intercept methods and, mainly, to those based on the use of the DR position.