American Association of Variable Star Observers

Lore & Background

After AAVSO's incorporation in 1918, it unofficially moved to Harvard College Observatory, which later served as the official AAVSO headquarters from 1931 to 1953. Thereafter, it moved around Cambridge before their first building was purchased in 1985: the Clinton B. Ford Astronomical Data and Research Center. In 2007, the AAVSO purchased and moved into the recently vacated premises of Sky & Telescope magazine. As of September 16, 2022, the Executive Director is Brian Kloppenborg. Before him, Kathy Spirer worked in this capacity for nine months, following the resignation of Styliani ("Stella") Kafka, who was in charge from February 2015 till the ember months of 2021. She succeeded Arne Henden. The previous director for many decades was Janet Mattei, who died in March 2004 of leukemia. The AAVSO currently has over 2,000 members and observers, with approximately half from outside the United States.

Reader's Guide

The AAVSO is significant because it fills a critical gap in astronomical research: professional astronomers lack the resources to monitor every variable star, so the organization enables amateurs to make substantial contributions. Its International Database (AID) stored over 35 million observations as of 2019, receiving nearly 1,000,000 annually from an estimated 2,000 observers. The International Variable Star Index (VSX), maintained by the AAVSO, cataloged 10,300,863 variable stars as of November 2023. The organization is quoted regularly in scientific journals. In education and public outreach, the AAVSO holds training workshops for citizen science and publishes papers with amateurs as co-authors. In the 1990s, it developed the Hands-On Astrophysics curriculum (now Variable Star Astronomy) with NSF support. In 2009, it received a three-year $800,000 NSF grant for Citizen Sky, a pro-am collaboration examining the 2009–2011 eclipse of epsilon Aurigae. The AAVSO's legacy includes the twenty-millionth observation received in its 100th year (2011) and the naming of minor planet 8900 AAVSO after the organization.

Did You Know?

• The AAVSO was founded in 1911 and incorporated in 1918.
• Its database held over 35 million observations as of 2019.
• Minor planet 8900 AAVSO is named after the organization.
• The AAVSO's first purchased building was the Clinton B. Ford Astronomical Data and Research Center in 1985.

Origins & Core Mission

The American Association of Variable Star Observers traces its roots to 1911, when a group of dedicated skywatchers banded together as an international nonprofit with a singular purpose: to systematically track how certain stars change in brightness over time. The organization's central function is to gather, analyze, publish, and archive observations—most of them contributed by amateur astronomers—so that meaningful light curves can be constructed. These light curves chart a star's fluctuations in luminance across days, weeks, or years, creating a visual record of its behavior. The AAVSO then makes these compiled records accessible to professional astronomers, researchers, and educators who might otherwise lack the means to monitor such objects themselves. In essence, the association serves as a vital bridge, transforming scattered individual measurements into a coherent scientific resource that supports the broader astronomical community.

The Scale of Citizen Science Data

One of the most striking aspects of the AAVSO is the sheer volume of data it has accumulated over more than a century. In 2011, marking the organization's centennial, the twenty-millionth variable star observation was logged into its database. By 2019, the AAVSO International Database had surpassed thirty-five million entries. The organization continues to receive roughly one million observations each year from an estimated two thousand contributors—both professional and amateur—who collectively feed this growing archive. The AAVSO also maintains the International Variable Star Index, a website that, as of late 2023, catalogs more than ten million variable stars. Because professional observatories simply cannot dedicate resources to watching every known variable star, astronomy stands out as one of the few scientific disciplines where amateur contributions remain genuinely significant to ongoing research. The AAVSO's data is regularly cited in peer-reviewed scientific journals, underscoring the real-world value of this grassroots effort.

Bridging Amateur and Professional Astronomy

The AAVSO has long championed the idea that citizen science and professional research are not separate endeavors but complementary ones. The organization routinely hosts training workshops designed to equip amateur observers with the skills needed for rigorous data collection, and it publishes scientific papers in which amateurs appear as co-authors alongside professionals. In the 1990s, with support from the National Science Foundation, the AAVSO developed a hands-on astrophysics curriculum that has since been rebranded as Variable Star Astronomy, bringing structured variable-star education into classrooms. A landmark moment came in 2009 when the NSF awarded the AAVSO a three-year, $800,000 grant to launch Citizen Sky, a pro-am collaboration project focused on studying the 2009–2011 eclipse of the star epsilon Aurigae. This project exemplified the organization's philosophy: by pooling the observational reach of amateurs with the analytical expertise of professionals, the AAVSO can tackle questions that neither group could address alone.

Institutional Journey & Enduring Legacy

The AAVSO's physical home has shifted many times, reflecting both growth and adaptation. The organization's earliest headquarters was simply the residence of founder William T. Olcott in Norwich, Connecticut. After incorporation in 1918, it unofficially relocated to Harvard College Observatory, which became its official seat from 1931 to 1953. Subsequent years saw the AAVSO moving around Cambridge before it finally purchased its first dedicated building in 1985, the Clinton B. Ford Astronomical Data and Research Center. In 2007, the organization acquired the recently vacated offices of Sky & Telescope magazine. Leadership has also evolved over the decades; Janet Mattei served as director for many years until her passing in March 2004, followed by Arne Henden, then Stella Kafka from 2015 to late 2021, a brief tenure by Kathy Spirer, and currently Brian Kloppenborg. The AAVSO's influence extends well beyond its walls: minor planet (8900) AAVSO bears the organization's name, and its publications—including the Journal of the AAVSO and the long-running AAVSO Circular—have shaped how variable-star data is shared worldwide.