With the many discoveries of variable stars, there quickly came to be far more work to do than there were professional astronomers available. It was Argelander, around the turn of the century, who suggested that amateurs might like to contribute observations to the study of variable stars. One important reason is that astronomers studying eruptive variables either at large ground-based observatories or from orbiting observatories need to be able to plan their observations. The association also publishes periodically monographs on selected stars. These are retained 2.
Many variables are irregular or semiregular, and there is no unique period or amplitude.
Eruptive - show sudden, unpredictable outbursts of light.