[Spice_discussion] Long-term accuracy of the IAU_MOON frame

John Irwin john at jir1667.plus.com
Mon May 11 08:59:33 PDT 2015

Just for everyone's reference I've plotted the difference between IAU_MOON
and the DE430/DE431 ME orientations, covering 1550-2550 for DE430 and
1000-2000 for DE431.


Red curve for the true difference sampled at 1-day intervals, the black
curve for a smoothed version (10-year sliding average). The results should
be accurate for DE430 but not-so-accurate for DE431 because I've assumed the
PA/ME offset for DE431 is the same as DE430. But for the period covered in
the plot I don't think it's a major issue.

As you can see the differences do not simply increase as one moves away from
2000. There are clear multiple periodic differences too where it is possible
for the discrepancy to reduce to nearly zero, even far from the year 2000.
But overall the difference is well within a kilometre. These differences are
almost entirely due to the limited harmonic content of the IAU_MOON model.


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