A third such position remains hidden behind the Sun at all times, and the idea of a hidden "Planet-X" there has been a staple of science fiction.
The first is always on the inward side of the secondary, and the second is on the outward side of the secondary.  A third such position remains hidden behind the Sun at all times, and the idea of a hidden "Planet-X" there has been a staple of science fiction. Four and five, the so-called Trojan points, lie along the orbit of the secondary around the primary. FTP, name these positions where the gravitational pull of the two large masses precisely equals the centripetal force required to rotate with them,  five points in the vicinity of two massive bodies--like the Earth and the Moon---where each others' respective gravities balance.
The first is always on the inward side of the secondary, and the second is on the outward side of the secondary.  
Lagrange points