Variable stars

Observing variable stars

Variable stars are stars that change brightness (most stars – including the Sun – vary in brightness if measured accurately). By studying their behaviour, much can be learnt about their physical properties such as size, mass, luminosity, temperature, structure, composition and evolution. This information can then be used to understand other stars.

Over 30 000 variable stars are known and many thousands more are suspected to be variable. Professional astronomers are not able to gather data on the brightness changes of thousands of variable stars; there are simply too many stars, and too few resources. Amateur astronomers, using visual, photographic, photoelectric and CCD techniques, can make significant contributions to science by observing these stars. Some 2 000 variables are suitable for visual monitoring in the southern hemisphere.

Visual estimates of magnitude are made by comparing the variable with two or more comparison stars, respectively brighter and fainter than the unknown variable. Suitable comparison stars are shown on special charts, which have been prepared for each variable star. The use of these charts is essential for accurate, standardized observations and intending new observers are therefore advised to obtain the necessary data by contacting the Variable Stars group of the Deep-Sky Observing Section.

The observed brightness estimates are used to generate light curves and are made available to a large number of professional observatories where astronomers are interested in investigating certain properties of the stars more fully.

Amateur observers also play an invaluable role by alerting the operators of orbiting satellite observatories whenever outbursts of certain eruptive variables are seen to occur, so that the orbiting observatories can be trained on the outburst for detailed study.