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American Association of Variable Star Observers (AAVSO)

The American Association of Variable Star Observers (AAVSO) is a non-profit worldwide scientific and educational organization of amateur and professional astronomers who are interested in stars that change in brightness--variable stars.

The AAVSO annual meeting, 1996.

The AAVSO was founded in 1911 at Harvard College Observatory to coordinate variable star observations made largely by amateur astronomers. In 1954, the AAVSO became an independent, private research organization. Today with members in 46 countries, and headquarters in Cambridge, Massachusetts, USA, it is the world's largest association of variable star observers.

The AAVSO coordinates, evaluates, compiles, processes, publishes, and disseminates variable star observations to the astronomical community throughout the world. The archives of the AAVSO currently contain over 9 million observations. Approximately 575 observers from around the world send over 300,000 observations each year. At the end of each month, incoming observations are sorted by observer and checked for errors. They are converted into computer readable form and processed using computer systems at AAVSO Headquarters. These observations are then added to the data files for each star in the AAVSO International Database. This database is a tribute to the skill, enthusiastic devotion, and dedication of AAVSO observers since 1911.

VSOCris.jpg vsomary.jpg   YOU can contribute significantly to the study of variable stars by making only a few hours of observations each month!
  • A telescope of any size or a pair of binoculars is sufficient equipment.
  • Long training and special skills are not necessary to begin variable star observing. As long as you take care to follow instructions, you can be making good observations after a few weeks of practice.
  • Beginning visual observers usually start with long period and semiregular variables. The large amplitudes and slow rates of variation of these stars make their observation an ideal means for observers to become experienced at making brightness estimates.
  • As observers gain experience, they often add to their programs other types of variable stars--cataclysmic variables, symbiotic stars, and R Coronae Borealis stars. These stars vary unpredictably, and--depending on their state of behavior--may require very frequent observations.
  • Some observers focus on eclipsing binaries or RR Lyrae stars. Observing these stars requires additional preplanning and special observing techniques.
  • Observers may also include in their programs systematic, regular searches for novae or supernovae
  • Once you begin, you will be sending your observations monthly to AAVSO Headquarters on special "report forms" by mail, fax, or electronically
  • Each year the AAVSO publishes the names of observers and the annual total of their observations in the Journal of the AAVSO .
  • There is no minimum monthly observation quota--even ONE observation is useful and significant!

Benefits of Membership

Members receive all the information and material needed to establish their own variable star observing program, subscriptions to the Journal of the AAVSO and the AAVSO Newsletter , and may choose from a large number of other publications available free of charge to members. Also, members receive notices of the semi-annual meetings of the AAVSO which they are encouraged to attend, and other mailings.

Services to the Observer

Gerry Dyck, AAVSO Member-Observer and Music Teacher, at his home-made telescope
The AAVSO enables variable star observers to contribute vitally to variable star astronomy by accepting their observations, incorporating them into the AAVSO data files, publishing them, and making them available to the professional astronomer. Incorporating an observer's observations into the AAVSO archives means that future researchers will have access to those observations, so the observer is contributing to the science of the future as well as the present. Also, the AAVSO coordinates observing runs between professional and amateur astronomers, in which observations from amateur astronomers play an important role in correlating observations obtained with special instruments at earth-based observatories or on board satellites.

Upon request, the AAVSO will help set up an appropriate observing program for an individual, an astronomy club, an elementary school, high school, or college, etc. In this way observers, students, and faculty are able to make the best use of their resources and to do valuable science. The AAVSO can also assist in teaching observing techniques and in suggesting stars to be included in a program.

Services to the Astronomical Community

AAVSO data, both published and unpublished, are made available to astronomers around the world. AAVSO services are sought by astronomers for:
  • Real-time, up-to-date information on unusual stellar activity;
  • Assistance in scheduling and executing of variable star observing programs using earth-based large telescopes and instruments on board satellites;
  • Assistance in simultaneous optical observations of program stars and immediate notification of their activity during earth-based or satellite observing programs;
  • Correlation of AAVSO optical data with spectroscopic, photometric, and polarimetric multi-wavelength data;
  • Collaborative statistical analysis of stellar behavior using long-term AAVSO data.
Collaboration between the AAVSO and professional astronomers for real-time information or simultaneous optical observations has enabled the successful execution of many observing programs, particularly those using satellites. A significant number of rare events have been observed with these satellites as a result of timely notification by the AAVSO.

Services in Education

Tal Mentall of the Amateur Telescope Makers of Boston introduces youngsters to astronomy through the AAVSO Partnership in Astronomy program.
For many years the AAVSO has been a source of information and guidance to students who decide to study variable stars for class or science fair projects. The AAVSO's most recent project in education is Hands-On Astrophysics--a curriculum for high school and college science and math classes which uses the AAVSO's unique variable star database. Also, its Mentorship Program connects experienced and enthusiastic variable star observers with anyone in their vicinity who is interested in learning how to become a better observer.

AAVSO Observing Programs

Visual: Most AAVSO observations are made visually. Stars best suited for visual observation have amplitudes of variation of more than one magnitude. The limiting magnitude of observations is 16.5 and the accuracy of the data is between ±0.2 and ±0.4 magnitude. The AAVSO Visual Observing Program includes about 3600 variable stars.

Photoelectric: Stars with small variations can be observed photoelectrically. The AAVSO Photoelectric Observing Program contains 50 bright, mostly red variables with less than 1 magnitude of variation. The photoelectric and the visual observing programs complement each other since most of these stars are also in the visual observing program. The accuracy of photoelectirc observations is ±0.008 magnitude.

Charge-Coupled Device (CCD): The minima of faint variables can be observed even with a small telescope equipped with a CCD. The CCD observing program consists of mostly long period variables in the visual program. Faint CCD observations complement both of the other observing programs of the AAVSO.

Divisions and Committees

Observations of most types of variable stars are coordinated and published by the Director and the technical staff at AAVSO Headquarters. Observing for certain types of stars is coordinated outside AAVSO Headquarters, under the authority of the AAVSO Director. These committees and divisions are:

Charge-Coupled Device
Photoelectric Photometry
Eclipsing Binary Stars
RR Lyrae Stars
Nova Search
Supernova Search
Solar Division

In addition, there is a New Charts Committee to oversee the preparation of new variable star charts and a Telescope Committee that is responsible for receiving and selling telescopes donated to the AAVSO. The Chairs of these committees operate volunatrily.

An AAVSO light curve of the variable star SS Cygni.

Membership in the AAVSO is open to anyone interested in variable stars and in contributing to the support of valuable research. Research on variable stars is important because it can provide much information--mass, radius, internal and external structure, composition, temperature and luminosity--about the properties of these stars. This information can then be extrapolated to other types of stars, including our Sun.

Amateur astronomers are making a real and useful contribution to science by observing variable stars and submitting their observations to the AAVSO International Database. They have both time and ready access to observing instruments needed to gather data on the brightness changes of thousands of variable stars.

In addition to contributing valuable observations, you can support the work carried on at Headquarters through your annual membership dues.

To become a member, or to obtain more information, please contact:

AAVSO Headquarters
25 Birch Street
Cambridge, MA 02138

Phone: 617-354-0484	Fax: 617-354-0665
email: aavso@aavso.org

Visit the AAVSO web site at http://www.aavso.org and visit the AAVSO Hands-On Astrophysics website at http://hoa.aavso.org

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