Milwaukee Astronomical Society


RR Lyrae Ephemeris

The MAS RR Lyrae Ephemeris provides the predicted time of maximum for a number of RR Lyrae and Delta Sct type stars. These times appear in Universal Time in the body of the ephemeris table. The time is rounded to the nearest half hour, providing sufficient accuracy to plan observing sessions while, hopefully, leaving sufficient doubt about the exact time in order to eliminate anticipatory bias. This ephemeris is designed for use by observers at American longitudes.

The top rows of the ephemeris table list the name of the RR Lyrae type star. Directly below the star's name are its approximate maximum and minimum magnitudes. These magnitudes are taken from the 4th edition of the GCVS and may be visual, photographic, or V.

Below that, in the row labeled "RISE". This is the approximate time required for the star to rise from minimum to maximum, in hours. By starting a observing run at least this many hours before the prediction, both the minimum and maximum may be observed.

CCD observations of RR Lyrae type stars at all phases of their lightcurves are encouraged. This ephemeris can be used as a guide to determine what portion of the lightcurve is observable on a given night.

The numbers in the left-most column are the "double date"—the evening and the following morning—for the event times listed in the corresponding row. For example, 5–6 corresponds to the evening of the 5th and the morning of the 6th of the month. January 0–1 is the evening of December 31 and the morning of January 1.

Click here for an introduction to the AAVSO: RR Lyrae Observing Program

These ephemerides are available by clicking on the links below. The data is presented in Adobe Acrobat format. The reader can be downloaded for free.

You can then print it out conveniently. If you have trouble getting an entire page printed out, check the "Fit to Page" selection on the print form. If your copy of Acrobat does not have this feature, download the latest version.

RR Lyrae Ephemerides *


Jan 2024
Feb 2024
Mar 2024
Apr 2024
May 2024
Jun 2024

Jul 2024
Aug 2024
Sep 2024
Oct 2024
Nov 2024
Dec 2024

* Please note: Ephemerides are published as they become available. Some links may not work correctly.