Astronomy’s Greatest Hits: The 100 Most Cited Papers in Each Year of the First Decade of the 21st Century (2000–2009)

Abstract

The first decade of the 21st century and the last few years of the 20th have been transformative for ground- and space-based observational astronomy due to new observing facilities, access to digital archives, and growth in use of the Internet for communication and dissemination of information and for access to the archives. How have these three factors affected the characteristics and content of papers published in refereed astronomical journals, as well as the journals themselves? In this and subsequent papers I will propose answers to this question. The analysis in this, the first paper of a series, is based on an examination of the 100 most cited papers in astronomy and astrophysics for each year between 2000 and 2009, inclusive, and supplemental data from 1995 and 1990. The main findings of this analysis are: Over the 10 yr period the total number of authors of the top-100 articles year(-1) has more than tripled. This increase is seen most strongly in papers with more than six authors. The number of unique authors in any given year has more than doubled. The yearly number of papers with five or fewer authors has declined over the same time period. Averaged over the 10 yr period the normalized number of authors per paper increases steadily with citation rank-the most highly cited papers tend to have the largest number of authors and vice versa. This increase is especially notable for papers ranked 1 through 20 in terms of number of citations and number of authors. The distribution of normalized citation counts versus ranking is remarkably constant from year to year and, except for the top-ranked half-dozen or so papers in each year, is very closely approximated by a power law. Nearly all of the papers that show the most divergence from the power-law fit-all in the sense of having a high number of citations-are based on the results of large observational surveys. Among the top-100 papers there is a small but significant correlation of paper length with citation rank. More striking, though, is that the average page length of the top-100 papers is one and a half times that for astronomy papers in general. For every year from 2000 to 2008, the same five journals account for 80 to 85% of the total citations for each year from all of the journals in the category of "Astronomy and Astrophysics" by ISI's Journal Citation Reports. These numbers do not include Nature or Science. Averaged over the 10 yr time period studied in this article, these same five journals account for 77% of the 1000 most cited papers, slightly less than the journals' fractional contribution to the total number of articles published by all journals. The five journals are A&A, AJ, ApJ, ApJS, and MNRAS. Two samples of the top-100 cited papers, both for the 6 yr from 2001 to 2006 but compiled 2.5 yr apart, show that a significant number of articles originally ranked in the top 100 for the year, drop out, and are replaced by other articles as time passes. Most of the dropouts address topics in extragalactic astronomy; their replacements for the most part deal with non-extra-galactic topics. Finally, some additional findings are noted that relate to the entire ensemble of astronomical journals published during the century's first decade. Various indicators of Internet access to astronomical Web sites such as data archives and journal repositories show increases of between factors of 3 and 10 or more. I propose that there are close complementarities between the communication capabilities that Internet usage enables and the strong growth in numbers of authors of th most highly cited papers. Subsequent papers will examine this and other interpretations of the analysis presented here in detail.