Definition Of apsis
either of two points on the orbit of a planet or satellite that are nearest to or furthest from the body around which it moves.
In particular there was, according to Aryabhata I, a basic period of 4320000 years called a mahayuga and it was assumed that the sun, the moon, their apsis and node, and the planets reached perfect conjunctions after this period.
Example Of apsis
At time II the line of apsides has turned through 90 degrees and we get a symmetric eclipse, indistinguishable from a circular orbit.
Because of gravitational disturbances by the other planets, the shape and orientation of the orbit are not fixed, and the apsides slowly move with respect to a fixed frame of reference.
Both the apsidal axis and the moon's nodal axis rotate.
By latus component we mean the component of the orbital velocity in the direction perpendicular to the apsidal axis of the orbit.
For the moon, the line of apsides completes one revolution around the sky in a period of 8.85 years.