American Association of Variable Star Observers (AAVSO)

An organization based in the USA for amateur observers of variable stars. It was founded in 1911 by William Tyler Olcott, who began making "volunteer" observations of the brightness of variable stars and sending his results to Edward C. Pickering at Harvard College Observatory after hearing a talk at the American Association for the Advancement of Science meeting in 1909. It has over a thousand members worldwide and a huge database containing millions of individual observations.