Except that "…due to nutation, an actual sidereal day is not quite so constant." Yeah. Nutation. Nutation "…is a rocking, swaying, or nodding motion in the ax

Except that "…due to nutation, an actual sidereal day is not quite so constant." Yeah. Nutation. Nutation "…is a rocking, swaying, or nodding motion in the axis of rotation of a largely axially symmetric object, such as a gyroscope, planet, or bullet in flight…" http://en.wikipedia.org/wiki/Nutation http://en.wikipedia.org/wiki/Nutation