An Anomalistic month is the time in which the moon passes from perigee to perigee, &c.
The problem of determining an orbit may be regarded as coeval with Hipparchus, who, it is supposed, found the moving positions of the apogee and perigee of the moon's orbit.
A line joining the moon in perigee and in apogee is called the " line of apsides."
In the case of the motion of the moon around the earth, assuming the gravitation of the latter to be subject to the modification in question, the annual motion of the moon's perigee should be greater by I 5" than the theoretical motion.
It may be considered as arising from a semi-annual variation in the eccentricity of the moon's orbit and the position of its perigee.