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Nelson Database of Eclipsing Binary O-C Files

Bob Nelson has developed over 5400 O-C (Observed - Computed) files of eclipsing binaries, all in Excel format, that we are hosting on our site. The purpose is to provide information on period variation for selected eclipsing binaries (for astronomers interested in a particular star) and to determine the best elements for predicting future eclipses.

The AAVSO Eclipsing Binary Ephemeris provides the predicted time of mid-eclipse for eclipsing binaries in the AAVSO Eclipsing Binary observing program. These times appear in Universal Time in the body of the ephemeris table. The time is rounded to the nearest half hour, which provides sufficient accuracy to plan an observing session while, hopefully, leaving sufficient doubt about the exact time in order to eliminate anticipatory bias. The ephemeris is designed for use by observers at American longitudes.