A Return to the Sumner Line?

Extract

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.