2005PASP..117..111T

In 2001, about 2100 papers appearing in 18 journals reported and/or analyzed data collected with ground-based optical and infrared telescopes and the Hubble Space Telescope. About 250 telescopes were represented, including 25 with primary mirror diameters of 3 m or larger. The subjects covered in the papers divide reasonably cleanly into 20 areas, from solar system to cosmology. These papers were cited 24,354 times in 2002 and 2003, for a mean rate of 11.56 citations per paper, or 5.78 citations per paper per year (sometimes called impact or impact factor). We analyze here the distributions of the papers, citations, and impact factors among the telescopes and subject areas and compare the results with those of a very similar study of papers published in 1990-1991 and cited in 1993. Some of the results are exactly as expected. Big telescopes produce more papers and more citations per paper than small ones. There are fashionable topics (cosmology and exoplanets) and less fashionable ones (binary stars and planetary nebulae). And the Hubble Space Telescope has changed the landscape a great deal. Some other results surprised us but are explicable in retrospect. Small telescopes on well-supported sites (La Silla and Cerro Tololo, for instance) produce papers with larger impact factors than similar sized telescopes in relative isolation. Not just the fraction of all papers, but the absolute numbers of papers coming out of the most productive 4 m telescopes of a decade ago have gone down. The average number of citations per paper per year resulting from the 38 telescopes (2 m and larger) considered in 1993 has gone up 38%, from 3.48 to 4.81, a form, perhaps, of grade inflation. And 53% of the 2100 papers and 38% of the citations (including 44% of the papers and 31% of the citations from mirrors of 3 m and larger) pertain to topics often not regarded as major drivers for the next generation of still larger ground-based telescopes.