Nelson Database of Eclipsing Binary O-C Files

The late Bob Nelson developed over 5800 O-C (Observed - Computed) files for eclipsing binaries, all in Excel format, which we are hosting on our site. The purpose of this database is to provide information on period variation for selected eclipsing binaries (for astronomers interested in a particular star), as well as to determine the best elements for predicting future eclipses. These elements go into eclipse prediction software, like at Shawn Dvorak's site (Bob and others help provide updated elements for Shawn).

For each star, they try to develop the best relationship possible; however, sometimes ambiguities arise. In these cases, the most likely set of elements are displayed. The files are updated about twice a year. Last Update: September 2023.

Most of the information used in creating these files came from the JAAVSO, Eclipsing Binaries Minima Database, IBVS, BAAVSS, BAVM, OEJV, VSB, and SIMBAD. Tom Krajci constructed over 30 of these files. Note the addition of GSC stars to the end of each constellation's list.

If you would like to help in maintaining the database, or want to contact the Database administrator, please contact Robert Jenkins at

For an Excel file containing data on over 10,000 eclipsing binaries, click here.

Database Access