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 light curve for exoplanet WASP-2b in Delphinus depicted below is one of the latest transitting exoplanets, having being announced in the fall of 2006, and which represents the second discovery of the WASP (Wide Angle Search for Planets) team. It is characterized with a mass 0.88 that of Jupiter and virtually the same size with a radius equivalent to 1.04 Jupiter radii and with a very brief orbital period of only 51.6 hours. WASP-2b requires only 108 minutes to transit its parent star at a depth of 1.90%. The parent star, GSC 522:1199, is estimated to have a mass of 0.79 solar masses, a radius equivalent to 0.78 solar radii, a temperature of 5,200° K and to lie at a distance of 493 light-years away with a visual magnitude of 11.98. The mass and size observed for WASP-2b in combination with its proximity to its hot parent star make WASP-2b a very typical example of a hot Jupiter. Further details regarding WASP-2 and WASP-2b are available in the paper published by the discovery team led by Collier Cameron et al (click here).

Note: The C- and K-stars used for the purposes of the differential photometry measurements depicted below were GSC 509:1844 (mag 11.03) and GSC 522:452 (mag 11.37) respectively.