Eclipsing Binary predictions and where to find them



The publication of Eclipsing Binary Predictions is now discontinued in the VSS Circular. Predictions for RZ Cas, Beta Per and Lambda Tau can still be found in the BAA Handbook. Predictions, completed on a monthly basis, are available on the BAA VSS website at:


If readers require paper copies of the predictions please contact me. The best source for predictions for Eclipsing Binaries is the Mt. Sahara Astronomical Observatory, Cracow Pedagogical University website (known as the Krakow website) at:


Click on ‘Constellation List’, choose your constellation and then choose your system. A webpage will then appear with lots of useful information regarding the system. In the section entitled ‘Light Elements’ there is a link entitled ‘current minima and phase’. When you click on this link, in the example of Beta Lyrae, you get predictions of primary and secondary eclipses for a period of three months. For systems with very short periods such as RZ Cas the predictions are for one week. For a system such as SW Cyg, with a period of around 4.57 days, the predictions are for a month.


The Krakow website does not tell you how much of an eclipse will be observable at a particular time of the year at your latitude and longitude. However, it has some useful literature references for each system, although they may not necessarily be up to date.  Nor are references to the ‘Information Bulletin on Variable Stars’ included, but these can be found at:


Although the Krakow website lists the depth of eclipses it does not list the actual V magnitudes at maximum and minimum. For an indication of these magnitudes you will need to visit the ‘General Catalogue of Variable Stars’ website at:


Click on ‘GCVS Query Form’, type in a designation such as SW Cyg, and click on ‘Search’. The resulting information displayed shows that maximum is 9.24V, primary minimum 11.83V, and secondary minimum 9.30V. These magnitudes, however, may have been determined some time ago.


The GCVS website gives SW Cyg a period of 4.57313411 days but the Krakow website lists the period of SW Cyg as 4.572986 days. The latter is more likely to list the most up to date period. It must always be borne in mind that small changes in a period can result in significant changes in the times of minima if the period was determined a few years ago.