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Any astronomers out there know what it would take to extend the pyephem library to enable it to calculate CMLIII for Jupiter? As of the current version it only calculates CMLI and CMLII

Thanks

Steve Berl
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All we would need are the constants for computing CML-III that match the constants we are already using for CML-I and CML-II, which you can find here in the source code:

https://github.com/brandon-rhodes/pyephem/blob/master/libastro-3.7.5/jupmoon.c#L199

If you can find a compatible pair of constants for CML-III, then we can add that number for Jupiter objects as well. Here you can find a Github issue where we will track whether this feature gets added:

https://github.com/brandon-rhodes/pyephem/issues/3

Brandon Rhodes
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What about using the conversion:

CMLIII=CMLII+81.2+0.266*(t-2438761.5)

which is defined for the conversion in Seidelman & Divine, "Evaluation of Jupiter Longitudes in System III(1965), Geophysical Research Letters, 4:65-68, 1977?

Linus Caldwell
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Tracy Clarke
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There is a Master's thesis by Rasha Hashim Ibrahim available at https://www.scbaghdad.edu.iq/library/Astronomy/MS.C/2011/Calculating%20the%20Central%20Meridian%20Longitude.pdf wherein he spells out the transformations between CML1, CML2, and CML3. I cannot vouch for its accuracy, but it appears to take a reasonable approach at the problem.

Ian Jordan
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  • The June 14, 2013 20:03/19:43 comment suggesting a simple formula for CMIII appears to contain an error for the period. The GRL paper is behind a paywall. – Ian Jordan Jul 12 '16 at 19:19
  • If one googles: "Jupiter compute CML III from CML I" a lower-down search return to the webpage [link] (http://www.projectpluto.com/grs_form.htm) gives a formula which appears to be very close to what i would expect when comparing it to graphs that SWIRI produced for events in mid-May 2016. The author on that site describes how he derived the equation, which seems reasonable. Notify @brandon-rhodes . – Ian Jordan Jul 12 '16 at 19:26