The AAVSO is a 501c(3) nonprofit organization whose worldwide scientific and educational activities focus on studying stars that change in brightness (variable stars) and other astronomical objects whose properties change over time.
Vision and Mission
The AAVSO’s Vision is to become the leading platform where people of all ages learn about and participate in scientific astronomy.
The AAVSO’s Mission is to provide amateur astronomers and students with the opportunity to make real and direct contributions to astronomy.
These guiding statements, adopted in early 2025, reflect a broader strategic direction for the AAVSO—one that embraces the evolving landscape of citizen science, the changing needs of professional astronomers, and the growing interests of our community. In line with this shift, our outreach and marketing efforts now emphasize that the AAVSO actively supports four core scientific focus areas:
- Stellar Photometry: Our foundational activity, ongoing since 1911
- Stellar Spectroscopy: Launched in April 2019, this program now hosts the second-largest collection of amateur astronomical spectra in the world.
- Exoplanet Photometry: Introduced in November 2018, this program supports NASA/JPL’s Exoplanet Watch initiative.
- Sunspot Counting: A long-standing program active since 1944.
AAVSO History
The AAVSO was founded in 1911 to coordinate variable star observations—made largely by amateur astronomers—for Harvard College Observatory. The AAVSO was incorporated in the Commonwealth of Massachusetts in 1918 as a non-profit scientific and educational organization and became independent from Harvard in 1953. In 1954 when the Johnson Amendment to the US Tax Code was adopted, the AAVSO became a 501(c)(3) organization.
With the growth of technology, interest, and opportunity for private individuals to participate in astronomical research in CCD, CMOS, DSLR, and PEP photometry, grating, slit, and echelle spectroscopy, and the detection and observation of exoplanets, the AAVSO has expanded its breadth and depth of connection to and involvement in the astronomical community. It also continues its decades-long work in the observation of sunspots and the production of the American Relative Sunspot Number.
Today, as an independent, private research organization headquartered in Cambridge, Massachusetts, with active participants in more than 100 countries, it is the world’s largest association of variable star observers and has an archive of over 69 million multicolor variable star observations. The AAVSO also has rapidly-growing archives of exoplanet observations and spectra of variable stars, as well as an ever-increasing archive of sunspot observations.
The AAVSO is also significantly expanding the opportunities it offers for learning about and participating in scientific astronomy.
Membership in the AAVSO is open to anyone—professionals, amateurs, and educators alike—interested in variable stars, exoplanets, spectroscopy of variable stars, or in the Sun, and in contributing to the support of valuable research and scientific astronomy.
Professional astronomers have neither the time nor unlimited access to equipment needed to gather data on the brightness and spectral changes of thousands of variables, follow up on ever-increasing numbers of exoplanets and potential exoplanet host stars, and monitor sunspots. Amateur astronomers make a real and useful contribution to science by observing targets in these categories and submitting their observations to the AAVSO’s databases. Non-observers may also contribute to science by supporting this work through AAVSO membership.