RESULTS IN MATHEMATICS, cilt.67, sa.3-4, ss.417-430, 2015 (SCI-Expanded)
In this paper, we investigate the focal surfaces obtained by the normal rectilinear congruence in the Minkowski 3-space. The sub-parabolic points and the ridge points are studied on the spacelike and timelike surfaces. We examine some special points on the surface, which form the sub-parabolic and the ridge lines in the Minkowski 3-space.