Birthday · September 9, 2026

Is this star winking at us? The central object in today’s animation is not one but two stars. XZ Andromedae, indicated by the bold lines, is an Algol-type eclipsing binary with a nearly edge-on orbit from Earth’s perspective. The bottom light curve shows the amount of light from the system dim and brighten as the cooler star eclipses its hotter, brighter companion. Analysis of several XZ Andromedae light curves indicates there may be two other stars orbiting the system. This particular light curve was created with Citizen Astronomy, an open-source software for differential photometry. The software takes the difference in brightness between a target and comparison star and traces its behavior over time. This technique reduces most variations from the instrument and Earth’s atmosphere. In addition to eclipsing binaries, this analysis is useful for studying transiting exoplanets, accreting black holes, supernovae, and many more time-varying astronomical phenomena. Astrophotographers: try it out on your own data!