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Let us set up a conventional Cartesian coordinate system
which is such that the (apparent) orbit of the
Sun about the EarthMoon barycenter lies in the

plane. This implies that the

plane corresponds to the socalled ecliptic plane. Approximating the solar orbit as a loweccentricity Keplerian orbit,
we can write
where
, and
is the orbital eccentricity (Yoder 1995). (See Section 4.13.) Here, we have
neglected terms that are
, and smaller.
Richard Fitzpatrick
20160331