  We report on the far-field photoluminescence intensity distribution of
interlayer excitons in MoSe$_{2}$-WSe$_{2}$ heterostacks as measured by back
focal plane imaging in the temperature range between 1.7 K and 20 K. By
comparing the data with an analytical model describing the dipolar emission
pattern in a dielectric environment, we are able to obtain the relative
contributions of the in- and out-of-plane transition dipole moments associated
to the interlayer exciton photon emission. We determine the transition dipole
moments for all observed interlayer exciton transitions to be (99 $\pm$ 1)%
in-plane for R- and H-type stacking, independent of the excitation power and
therefore the density of the exciton ensemble in the experimentally examined
range. Finally, we discuss the limitations of the presented measurement
technique to observe correlation effects in exciton ensembles.
