The prediction service of H. M. Nautical Almanac Office

Abstract

Most people think that close artificial satellites of the earth fall directly within the field of responsibility of H. M. Nautical Almanac Office. This is not so. The Office, and the corresponding ephemeris offices in other countries, are concerned primarily with long-term, high-precision theories and predictions of heavenly bodies; comets and meteors are excluded from our field and are dealt with com­petently by others, mainly by amateurs. Our professional interest will be aroused when an artificial satellite is launched into an orbit with perigee so high above the earth’s surface that atmospheric drag is very small; such an object, with a life of ten years or more, will be of definite astronomical importance. The ephemeris offices will then produce, and publish, accurate ephemerides based on a combina­tion of theory and observation to assist in the comparison of theory with observa­tion. It is conceivable that such satellites will provide rapid and accurate methods for the determination of the second of ephemeris time, now accepted as the funda­mental standard of time. Navigational applications must also be considered. For the two satellites so far (29 November) launched by U. S. S. R., the Office has been compelled, through limitations of staff and equipment, to confine its work to ( a ) a prediction service, and ( b ) the collection and copying of observations and their transmission (in due course) to I. G. Y. World Data Centres, and possibly directly to other institutes.