  Isophote comprises a locus of the surface points whose normal vectors make a
constant angle with a fixed vector. In this paper, isophote curves are studied
on timelike surfaces in Minkowski 3-space E31. The axises of spacelike and
timelike isophote curves are found via their Darboux frames. Subsequently, the
relationship between isophotes and slant helices is shown on timelike surfaces.
