8 July 2020

Another Strong Showing for AAS Journal Metrics

Here's some good news from AAS Publishing: Our peer-reviewed journals remain among the highest-ranked publications in the astronomical sciences according to several key metrics.

The impact factor of the Astronomical Journal (AJ) rose 6.2% from 5.497 in 2018 to 5.838 in 2019, and that of the Astrophysical Journal (ApJ) rose 3.0% from 5.580 to 5.745. Not only is the AJ's impact factor higher than it has ever been, but for the first time, it is higher than the ApJ's. This is undoubtedly a consequence of our introduction of topical corridors to the article-submission process. Now, instead of selecting which AAS journal to submit your article to, you choose the appropriate topical corridor, and our editorial team decides which journal best suits it. The ApJ's impact factor has risen slowly but steadily since the change, whereas the AJ's — which we felt was lower than it should have been — has increased substantially. This year's 6.2% improvement follows a whopping 32% jump last year. We certainly expected the AJ's impact factor to benefit from the change in how we process manuscripts, but we never imagined that it would match, and even exceed, the ApJ's so quickly.

AJ and ApJ Family

In case you're new to the impact factor, it's one of several quantitative tools used to evaluate journal quality. It measures the frequency with which the average article has been cited during a particular period. Compiled annually for nearly 12,000 journals by Clarivate Analytics' Web of Science Group, the impact factor is calculated by dividing the number of citations in the most recent full year to the articles published in that journal during the previous two years. So, using the numbers above, in 2019 the average AJ article from 2017-2018 was cited 5.838 times, and in 2019 the average ApJ article from 2017-2018 was cited 5.745 times.

Among all our journals, the Astrophysical Journal Letters (ApJL) has the highest impact factor, 8.198. That's slightly lower (2.1%) than last year's 8.374, but still solidly out in front of our other titles. This reflects the Society's continuing dedication to ApJL's mission of rapidly publishing articles of great interest and great significance to the astronomical community. Another likely factor is the publication of "focus issues" featuring collections of papers on special topics.

The other member of the ApJ family, the Supplement Series (ApJS), saw a 4.3% decrease in impact factor from 8.311 in 2018 to 7.950 in 2019 — putting it slightly below ApJL. We think this decline, like the 2.9% one the previous year, results from ApJS publishing fewer and generally longer and/or more data-intensive articles than our other journals, such that the presence (or absence) of a small number of highly cited papers can skew the impact factor up or down.

Our newest peer-reviewed journal, the Planetary Science Journal (PSJ), won't have an impact factor for at least a couple more years, because its first articles didn't appear until early 2020.

The Astronomical Journal and all members of the Astrophysical Journal family occupy four spaces in the list of the top 10 journals in astronomy and astrophysics. Nature Astronomy (impact factor 11.518) is ahead of us, whereas Astronomy & Astrophysics (5.636) and Monthly Notices of the Royal Astronomical Society (5.356) are behind us.

The impact factor is just one of many different metrics by which journals are judged, rated, and ranked. Among those used by Google Scholar is the h5-index. This is the largest number h such that h articles published in the last five full calendar years (e.g., 2015-2019) have at least h citations each. In astronomy and astrophysics, our own ApJ (including ApJL) tops the list at 167. ApJS and AJ occupy the 5th and 6th spots, respectively.

Earlier this year, Nature Index published an article entitled "These Four Journals Publish the Most Nobel Prize-Winning Papers in Physics." It reported that Nobel Prize-winning research isn't always published in the highest-impact journals: "Physical Review Letters published by far the most award-winning research, accounting for 28.5% of the Nobel Prize-awarded papers, followed by the Astrophysical Journal (11.2%), Science (5.6%), and Nature (4.7%)." The author of the study described in the article, Rasmus Bjørk (Technical University of Denmark), commented, "This is contrary to the journals' respective impact factors, where Physical Review Letters and the Astrophysical Journal have much lower impact factors than Nature and Science."

AAS Publishing would like to take this opportunity to thank our journals' readers, authors, and reviewers, as well as our hard-working team of editors. Together we continue to support the AAS mission to enhance and share humanity's scientific understanding of the universe.

The AAS Publishing Team

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