A variable star, as its name suggests, is a star whose magnitude varies intrinsically, in contrast to eclipsing binaries whose magnitude varies as a result of one star in the binary system eclipsing the other. True variables are one of five types, namely Mira stars, semiregular stars, cepheids, eruptive variables and, finally, cataclysmic variables. Minimum to maximum magnitude can range from days to many months with some variables displaying irregular periods.

A popular method for the study of variable stars, particularly short-term variables, is by the use of the technique known as "differential photometry". Rather than measure the (variable) magnitude of a variable star on an absolute scale, measurements are made over time relative to one or more non-variable star(s) and these differences are then plotted so as to study and illustrate the relative or differential change in magnitude. Due to the very large number of variables stars, the field of differential photometry represents one of the key fields in astronomy whereby the amateur astronomer can make a meaningful and long-lasting contribution to both science and astronomy.

More recently, the search for extrasolar planets (over 750 discovered so far) has identified yet another interesting application for the practice of differential photometry whereby the minute drops in magnitude of a star hosting an exoplanet are studied. Further details for the interested party are available here.

Note: The eclipsing binary star DR Vul is a quick eclipsing binary variable star with a period of 2.2508645 days and which involves a delta mag of 0.62 (v) magnitudes during this brief time interval. The variable nature of DR Vulpeculae was discovered by C. Hoffmeister in 1935 whereas its period was established by V.P. Tsesevich in 1954. DR Vulpeculae is an Algol-type eclipsing system where the binary components involve main sequence stars with spherical or slightly ellipsoidal components and, hence, for its classification, namely "EA/DM". Longterm studies have identified an apsidal motion involving a period of 37.8 years as well as variable depths for both primary and secondary minima. For the latter, it has been suggested that a third star may be directly responsible for this inconsistancy (see O'Connell, 1972). Further details from the International Variable Star Index are available here whereas an AAVSO finder chart is available here.

Note: The minimum observed below is a secondary minimum.