Astronomical Almanac

The Astronomical Almanac is an almanac published by the United States Naval Observatory (USNO) and Her Majesty's Nautical Almanac Office (HMNAO); it also includes data supplied by many scientists from around the world. It is considered a worldwide resource for fundamental astronomical data, often being the first publication to incorporate new International Astronomical Union resolutions. The almanac largely contains solar system ephemeris and catalogs of selected stellar and extragalactic objects. The material appears in sections, each section addressing a specific astronomical category. The book also includes references to the material, explanations, and examples. It is available one year in advance of its date.

The Astronomical Almanac Online is a companion to the printed volume. It is designed to broaden the scope of the publication, not duplicate the data. In addition to ancillary information, the Astronomical Almanac Online extends the printed version by providing data best presented in machine-readable form.

The Explanatory Supplement to the Astronomical Almanac, currently in its third edition (2013), provides detailed discussion of usage and data reduction methods used by the Almanac. It covers its history, significance, sources, methods of computation, and use of the data. Because the Astronomical Almanac prints primarily positional data, this book goes into great detail on techniques to get astronomical positions. Earlier editions of the supplement were published in 1961 and in 1992.

Section A: PHENOMENA includes information on the seasons, phases of the Moon, configurations of the planets, eclipses, transits of Mercury or Venus, sunrise/set, moonrise/set times, and times for twilight. Preprints of many of these data appear in Astronomical Phenomena, another joint publication by USNO and HMNAO.

Section B: TIME-SCALES AND COORDINATE SYSTEMS contains calendar information, relationships between time scales, universal and sidereal times, Earth rotation angle, definitions of the various celestial coordinate systems, frame bias, precession, nutation, obliquity, intermediate system, the position and velocity of the Earth, and coordinates of Polaris. Preprints of many of these data also appear in Astronomical Phenomena.

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