تسجيل الدخول

تسجيل

Positions, motions and coordinate systems

المؤلف:  James Binney and Michael Merrifield

المصدر:  GALACTIC ASTRONOMY

الجزء والصفحة:  p-27

2026-09-08

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Positional astronomy, or astrometry, is the oldest branch of astronomy. Catalogs of the locations of astronomical objects on the sky have come down to us from antiquity. It is probably fair to say that astrometry was the central problem of observational astronomy through the early twentieth century. Later in the twentieth century, astrophysical observations attracted more interest and generated more excitement than astrometry, to the extent that students sometimes have the (mistaken) impression that positional astronomy is old fashioned and even unimportant. Such an opinion is grievously wrong, not only because the data obtained by astrometric measurements lie at the foundation of all astrophysics, but also because in recent years the subject has undergone a renaissance. Technological advances that got under way around 1980, have spectacularly improved the accuracy, homogeneity, and extent of the available astrometric data. In 1997 the field was revolutionized by the publication of the Hipparcos Catalogue, which is based on data taken by the first astrometric satellite; the catalog contains data of unprecedented homogeneity and accuracy for more than 100000 nearby stars. These new data will over time have a profound influence on almost every branch of astrophysics, from stellar astronomy to cosmology.

The issues that positional astronomy deals with are anything but trivial. Among them is the task of establishing in practical terms, an inertial reference frame. Extensive discussions of this problem can be found in Green (1985), Perryman et al. (1997), Seidelmann (1992) and Murray (1983). In our treatment of this subject we start by studying how astronomers report the positions and motions of objects on the sky.