The RHO web server hosts online interactive applications that calculate eclipsing binary (EB) and RRLyrae star events for a user-specified data and location. The EB program determines which eclipsing binaries will undergo an eclipse visible from the specified location on the given date, and the RRLyrae program does the same determination for times of maxima (ToMx) for RRLyrae stars. The applications can be accessed through the following links:

  EB ephem generator
  RRLyrae star ephem generator.

The original data source for both applications was the master list of variable stars, the General Catalog of Variable Stars (GCVS). The data for both applications has been further enhanced with times-of-minima (ToMs) and updated periods from a variety of sources, including the AAVSO and Milwaukee Astronomical Society (MAS), observations from the RHO, and papers in various journals. Many stars have been under-observed for decades, with many of them lacking any published observations since their original discovery decades ago. As improved ToMs and epochs for these become available the databases are updated to provide more accurate event predictions.

The two applications have very similar appearance and operation. The initial of each has fields to input the user's time zone and location, the target date, and limits for magnitude and declination. Clicking the "Submit" button sends query to the server, and a results page is returned.

The results page lists all stars that meet the declination and magnitude limits, and are above the minimum altitude limit of 30° during darkness at the target location. Each star name is a link to a page that provides detailed information on that star. The Date/Time column shows the time-of-minimum for EBs (maximum eclipse) or time-of-maximum for RRLyrae stars. The Altitude and Azimuth columns display the horizon coordinates corresponding to the Date/Time. The Duration column provides an idea of how long the eclipse or maximum lasts, and is a rough estimate of how long to observe to get useful results. The Cycles column reports the number of orbits (EBs) or pulsation cycles (RRLyraes) have occurred since the epoch in the database. This is an indication of the accuracy of the prediction and the importance of observing the target. Large cycle counts generally mean lower accuracy in the timing of the predicted event since there's been more time for errors in the period to accumulate. Stars with large cycle counts are also ones that should be higher priority since they've been neglected.