In connection with photodissociative spectroscopy, where one studies the anisotropy of the velocity vectors of photodissociated fragments, one can derive an expression for the anisotropy of flux depending on the angle between the transition dipole moment and the direction of travel of the dissociated fragment. The formulas derived here correct the simple derivations for the effect of rotation and finite dissociation velocity. The loss of anisotropy for a finite velocity is proportional to the ratio of thermal energy to translational dissociation energy.