Solar Section        


Solar Ephemeris and Commencement dates/times for Carrington Rotations


Several factors play a role why we do not see the Central Meridian and Equator of the Sun lined up in the center of the face of the Sun when we make our observations from Earth. Such factors include the tilt of the Sun relative to our orbit, as well as the rotation of the Sun corrected for the slightly elliptical orbit of Earth around the Sun. In order to determine exactly the location of a feature on the Sun, we need to consider these deviations in determining the true heliographic coordinates of the features:

  • Lo – the heliographic longitude of the center of the disk – this decreases by an average value of 13.2° per day,
  • Po – the position angle of the north end of the axis of rotation, measured + if east of the north point of the disk,
  • Bo – the heliographic latitude of the center of the disk,
  • Diameter the apparent diameter of the Sun

A resource we provide, is the beginning date/time of Carrington Rotations. Contrary to Bartel’s Rotations, Carrington Rotations start at odd times during the day. In order to identify your observation with the correct CR Number, please consult the short file for commencement dates and times for the CRs between 2015 and 2025, or CR2159 to CR2306.

For longer term analysis or research, we also provide a file containing the same data for rotations between 1853 and 2083 or the Rotations CR-10 and CR3082.

Since the ephemeris change with time especially the Po (approx. 1/2 degree per hour), the tools WIMP and Winjupos have been very valuable in determining these exact values at the time of your observations. Both programs are free and can be downloaded to your PC.

For Winjupos go to and click the download link in the left column.

WIMP can be downloaded from the Mars Observer’s Café Site, as well as the A.L.P.O. Computer Section.

In case you need access to the old ephemeris page, please click this link .

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