American Association of Variable Star Observers

The American Association of Variable Star Observers brings amateur and professional astronomers together to study the changing light from other stars. The AAVSO’s members have spent the past century making important contributions to science that professionals cannot make on their own. 

Stars twinkle in the night sky thanks to turbulence in the atmosphere. That’s one of the reasons space agencies put telescopes in space. But even then the light from distant stars isn’t constant. Starlight brightens and fades over time. It may take millions of years as a star ages or it may happen in minutes. Some of the variation is due to the nature of the star. Nuclear fusion in a star’s core may make the star throb. As it grows and shrinks, the light from the star dims and brightens. In other cases two stars may orbit each other so closely and from such a distance that their light merges into a single point in our night sky. The light from one of these binary stars is blocked as it passes behind the other, reducing the combined light arriving at Earth. Planets circling other stars block light as their orbit carries them between the star and the Earth.

Observing variable stars is like observing the tides. If you sit on a dock and measure the sea’s level over the course of the day, you can chart the rise and fall of high and low tides. You see how the patterns change as the Moon orbits Earth by observing the tides over the course of months and years. Variable star astronomers do the same thing by measuring a star’s brightness over time. They display the data as a light curve that shows the rising and falling brightness levels over time. That pattern gives astronomers insights into the nature of a variable star’s properties.

The economics and culture of professional astronomy works against professional astronomers who want to study variable stars. The allocation committees at professional observatories don’t like research projects that monopolize the telescopes’ observing time. Grant committees increasingly focus on projects that can deliver the biggest impact within their grant cycles. Variable star observing requires many observations to build a light curve that captures the star’s full cycle. That can take time as the vagaries of weather, poor seeing conditions, and other factors make some nights useless for making observations. That’s where the amateurs at the AAVSO come in.

Established in 1911, the AAVSO has hundreds of amateur members around the world. On any given night there are clear skies somewhere on Earth where these amateurs can make their observations. Through their own research and in cooperation with professional researchers, the AAVSO’s members add one million observations a year to its database which now has over twenty-five million observations of thousands of variable stars. The database’s quality makes it a valuable resource for professional astronomers who use the data in their research.

The professionals also turn to AAVSO members to make new observations that support their research projects. Observations made by a small team of amateurs from around the world lets the professionals build light curves much faster - and for much less money - than they could on their own. The AAVSO has a formal system in place for professional astronomers to ask for help from amateurs. Professionals submit an Alert Notice that the AAVSO distributes to its members. Amateurs interested in the research then work with the professionals to collect the needed data. 

Researchers at the Hubble Heritage Project, for example, turned to AAVSO members in 2010. The Project’s job is to connect the public to the space telescope’s scientific results. They wanted the AAVSO’s help to observe M31-V1, a Cepheid-class variable star in our neighboring Andromeda Galaxy. Edwin Hubble’s observations of M31-V1 in 1925 confirmed that other galaxies exist beyond the Milky Way - an important historical milestone in modern astronomy. Since professionals hadn’t studied M31-V1 much since Hubble’s original observations, the Hubble Heritage Project proposed using the space telescope that bears Hubble’s name to commemorate the discovery. Hubble’s review committees wouldn’t normally approve this kind of proposal - variable star astronomy isn’t what the telescope was built for. The public outreach value was enough to justify giving the team some of Hubble’s time - but only enough to make four observations. The team submitted an AAVSO Alert in July 2010 to confirm the timing of M31-V1’s variations so they could schedule Hubble’s observations correctly. Modern amateur telescopes and CCD sensors let these amateurs reproduce the observations Edwin Hubble made with the multi-million dollar Hooker Telescope nine decades earlier. The amateurs produced over two hundred observations within six months which let the Hubble Heritage Team make their space observations. You can read the Hubble Heritage Project’s announcement of the observations or watch the press conference they conducted at the American Astronomical Society’s May 2011 meeting. The peer-reviewed paper “Modern observations of Hubble's first-discovered Cepheid in M31” appeared in the Publications of the Astronomical Society of the Pacific. (doi:10.1086/663651 or arXiv:111.0262)

The AAVSO has several observing sections that coordinate different kinds of observations. The High Energy Network, for example, conducts follow-up observations of gamma-ray bursts detected by space telescopes. The Catastrophic Variable Section focuses on novae, the sudden blasts of matter and energy from white dwarf stars in binary star systems. The Solar Section studies variations in our own star. While not as extreme as other variable stars, the Sun’s light does change as sunspots form on its surface. When the Second World War disrupted sunspot reports from Switzerland, the Solar Section of began its own sunspot counting project. Over 100 amateur and professional astronomers now maintain the historical sunspot record - an important reference for scientists studying the Sun and its influence on Earth’s climate. The Solar Section also has members who build their own radio telescopes to study the effect of solar flares on Earth’s geomagnetic field in the AAVSO’s Sudden Ionospheric Disturbances Program.

The AAVSO encourages its members to submit papers based on their own data or on data from the association’s database. Tutorials on the AAVSO website guide new members through the process of analyzing data and publishing the results in the peer-reviewed Journal of the American Association of Variable Star Observers. Professional catalogs index the Journal due to the quality of the work it publishes.

The AAVSO’s long history of accomplishment in variable star astronomy is only possible because it actively recruits new members. The Citizen Sky project, for example, enlisted hundreds of novice astronomers into a worldwide effort to study the variable binary system epsilon Aurigae. Over the course of two years the amateurs contributed over eight thousand observations to make epsilon Aurigae the most thoroughly-observed variable star in history. Citizen Sky is now the AAVSO’s introductory program for new variable star astronomers and provides an easy onramp to making real scientific contributions to astronomy.