Positions of the moons of Pluto during the New Horizons flyby
At the time of closest approach to Pluto, Nix was on the same side of Pluto as New Horizons; all the other moons were farther away. Consequently, New Horizons' best images of smaller moons are of Nix. Note that the moment of closest approach is not the same as the moment of the moon-plane crossing. When New Horizons crossed the plane containing the moons' orbits, it was at a distance from Pluto near Charon's orbit.
This image is in the public domain.
Original image data dated on or about July 14, 2015