Lunar apsidal precession relative to equinox

[fizzy]

The period of the lunar apsidal precession is about 8.8506 years measured against fixed starts. How can I accurately convert this to the period between alignments with spring equinox?

Thanks.

 

[fizzy]

since lunar apsidal precession is prograde and general precession ( equinox ) is retrograde, is this correct?

1/(1/pApsidal + 1/25772.)

1/(1/pApsides +(1-Sidereal_year/Tropical_year))