Variable stars are, quite simply, stars that change brightness.
More than 30,000 are known and catalogued, and many thousands more are suspected variables. Such instruments enable us to probe many different regions of the spectrum, such as X-ray, ultraviolet, infrared, and radio wavelengths. The data obtained with special instruments and in shorter or longer wavelengths are compared with optical measurements, which serve as a benchmark. To date, the vast majority of long-term data has been provided by amateur observers . The light curve is the single most important graph in variable star astronomy.