Use of astronomical literature—A report on usage patterns☆

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Abstract

In this paper we present a number of metrics for usage of the SAO/NASA Astrophysics Data System (ADS). Since the ADS is used by the entire astronomical community, these are indicative of how the astronomical literature is used. We will show how the use of the ADS has changed both quantitatively and qualitatively. We will also show that different types of users access the system in different ways. Finally, we show how use of the ADS has evolved over the years in various regions of the world.

Introduction

The SAO/NASA Astrophysics Data System (hereafter ADS), is a digital library and a vital source for bibliographic information in astronomy. The vast majority of astronomical researchers in the world use the ADS on a daily or near-daily basis. The use of the ADS has not only changed quantitatively but also qualitatively. Initially almost exclusively used by professional astronomers, the ADS now also has become a public service through external, general search engines (like Google, Yahoo, Microsoft Live Search and Ask.com, to name a few). Henneken et al. (2007) observed that up to the middle of 2004, the number of ADS users doubled on a bi-yearly basis. Since the ADS started to be indexed by general search engines, the number of incidental users have increased dramatically. However, the number of typical users (more than 10 visits per month) has continued to follow the same growth pattern.

With different types of users come different types of use. A professional astronomer has different interests than an occasional user. One way of illustrating this is to look at the distribution of publication years for the literature people are interested in. We will also look at the diversity of ADS users from a geographical point of view. This will indicate whether increased Internet access actually results in an increase of ADS usage. This is particularly interesting with respect to aspects of the “Digital Divide” (see e.g. ITU, 2007). In the next section, we will describe the character of the data we are working with. The following section will show the results, which will then be discussed in Section 4.

Section snippets

Data

The ADS is an electronic library where the system log files record queries and access to its records over time. For every bibliographic record in the ADS, a user can choose to view or access various types of metadata associated with that record. A “visit” (or “read”) is defined as the selection of a metadata link. The ADS’s data log entries record what type of data item was selected for which article. For example, in the period of January and February of 2008, 72% of all requests were for an

General readership

Fig. 1 (top) illustrates the observation we made in Section 1 “Since the ADS started to be indexed by general search engines, the number of incidental users has increased dramatically”. The line marked ‘+’ shows the total number of users. This includes incidental users who just look at an abstract. Excluding incidental users, the total number of users is shown by the line marked with ‘×’ (these users request additional metadata, besides abstracts, and perform queries). Finally, the number of

Discussion

Fig. 1 shows how the ADS has become a public service whose reach goes well beyond the scholarly community. Since 2005, the number of people visiting the ADS via external sites has increased dramatically. This aspect will only intensify with the advent of the World Wide Telescope (Gray & Szalay, 2002), which has links to the ADS. Google Sky (Scranton et al., 2007) already contains context-sensitive menus that enable positional searches for papers in ADS. Incidental users have contributed the

Conclusions

In terms of its audience, the ADS has not only changed quantitatively, but also qualitatively. Besides a steady growth of the ADS regular users, we observe a dramatic increase in incidental users. The ADS is per definition the gateway to online literature for scientists, used by virtually all professional astronomers on a daily basis. Since 2005 there is a growing role as a source of science education of the general public.

Comparing the group of “ADS regulars” with the group visiting the ADS

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The ADS is funded by NASA Grant NNG06GG68G.

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