The NASA Astrophysics Data System: Overview

The NASA Astrophysics Data System Abstract Service has become a key component of astronomical research. It provides bibliographic information daily, or near daily, to a majority of astronomical researchers worldwide. We describe the history of the development of the system and its current status. Urania (Boyce 1996), and the ADS role in the emerging electronic astronomical data environment are discussed. Astronomy is unique in that it already has a fully functional data resource, where several of the most important data sources exist on-line and inter-operate nearly seamlessly. The ADS and the Strasbourg Data Center (CDS; Genova et~al. 2000) form the core of this resource. We show several examples of how to use the ADS, and we show how ADS use has increased as a function of time. Currently it is still increasing exponentially, with a doubling time for number of queries of 17 months. Using the ADS logs we make the first detailed model of how scientific journals are read as a function of time since publication. We find four distinct components. We directly compare the readership rate with the citation rate for scientific articles as a function of age. Citations generally follow reads, but there are some differences. The main journals of astronomy have differences in the ways they are read and cited. We discuss these from a number of different aspects. The impact of the ADS on astronomy can be calculated after making some simple assumptions. We find that the ADS increases the efficiency of astronomical research by 333 Full Time Equivalent (2000 hour) research years per year, and that the value of the early development of the ADS for astronomy, compared with waiting for mature technologies to be adopted, is 2332 FTE research years. A full technical description of the ADS is in three companion articles: \cite{gei}, \cite{aa}, and \cite{csg}. The ADS is available at http://adsabs.harvard.edu/.