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 (700 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-3b in Lyra depicted below is one of the latest transiting exoplanets, having being announced in early 2008, and which represents the third discovery of the WASP (Wide Angle Search for Planets) team. It is characterized with a mass nearly twice that of Jupiter and a very brief orbital period of only 44.3 hours. WASP-3b requires 160 minutes to transit its parent star at a depth of 1.14%. The parent star, GSC 2636:195, is estimated to have a mass of 1.24 solar masses, a radius equivalent to 1.31 solar radii, a temperature of 6,400° K and to lie at a distance of 727 light-years away with a visual magnitude of 10.64. The high mass observed for WASP-3b in combination with its proximity to its hot parent star make it one of the largest and hottest exoplanets discovered so far. The light curve below is characterized with a slight increase in brightness following egress and which has been observed elsewhere as well, thus suggesting the possible existence of a ring system leading to forward scatter. Further details regarding WASP-3 and WASP-3b are available in the paper published by the discovery team led by Don Pollacco et al (click here).

Note: The C- and K-stars used for the purposes of the differential photometry measurements depicted below were GSC 2636:140 (mag 11.10) and GSC 2636:145 (mag 12.0) respectively.