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S. E. Urban (USNO), S. Bell (HMNAO), G. H. Kaplan (USNO), C. Y. Hohenkerk (HMNAO), S. G. Stewart, J. A. Bangert, J. L. Hilton (USNO)
Over the last few decades, advances in the precision of astronomical and geophysical measurements along with improvements in the underlying theories have lead astronomers to realize that better models and computation methods -- and detailed specifications on how to apply them -- were necessary. This work culminated in several resolutions that were adopted by the International Astronomical Union (IAU) in 1997 and 2000. These include changes to the fundamental celestial reference system, changes to time-scales used in astronomy, new models of precession and nutation, and a new method of computing Earth rotation.
Among the first places astronomers will notice the influence of the resolutions is in The Astronomical Almanac (AsA), produced jointly by the U.S. Naval Observatory (USNO) and Her Majesty's Nautical Almanac Office (HMNAO). Due to the breadth of the changes and the required lead time, the 2006 edition is the first to have the data consistent with the resolutions. Much of the 2006 AsA is based on new software -- the IAU SOFA package for the data prepared by the British, and a considerably updated NOVAS package for the American portion -- and much new text has been included that describes the new formulations and paradigms. Since the AsA has page limitations, a practical explanation about the resolutions and how to implement them are addressed in detail in a separate publication, USNO Circular 179 (http://aa.usno.navy.mil/publications/docs/Circular_179.html). This paper will discuss specific changes in the The Astronomical Almanac 2006 and identify resources for additional information.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.