The AAVSO Argelander Society

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Friedrich Argelander was the first astronomer to begin a careful study of variable stars. At the time, only a handful of variables were known, and he was responsible for introducing the modern system of naming them using the capital letters R-Z. It was believed that variability was a rare phenomenon and that this would provide plenty of names for the variables yet to be discovered. In a few years this proved inadequate and the naming system was extended to double letters, and then a numbering system. Today, tens of thousands of variable stars are cataloged, with more being discovered all the time.

The “Argelander Step Method” is a visual method of estimating the magnitude of a variable star. It involves comparing the variable with comparison stars of known constant magnitude, and assigning a step value that reflects the brightness of the variable as distinguished from that of the comparison star. The magnitude of the variable can then be calculated from the known magnitudes of the comparisons. This is very similar in practice to methods still used today by visual observers of variable stars.