  Interstellar neutral hydrogen flows into the heliosphere as a mixture of the
primary and secondary populations from two somewhat different directions due to
splitting occurring in the magnetized outer heliosheath. The direction of
inflow of interstellar neutral H observed in the inner heliosphere, confronted
with that of the unperturbed flow of interstellar neutral helium, is important
for understanding the geometry of the distortion of the heliosphere from axial
symmetry. It is also needed for facilitating remote-sensing studies of the
solar wind structure based on observations of the helioglow, such as those
presently performed by SOHO/SWAN, and in a near future by IMAP/GLOWS. In the
past, the only means to measure the flow direction of interstellar hydrogen
were spectroscopic observations of the helioglow. Here, we propose a new method
to determine this parameter based on a long series of photometric observations
of the helioglow. The method is based on purely geometric considerations and
does not depend on any model and absolute calibration of the measurements. We
apply this method to sky maps of the helioglow available from the SOHO/SWAN
experiment and derive the mean flow longitude of interstellar hydrogen. We
obtain $253.1\degr \pm 2.8\degr$, which is in perfect agreement with the
previously obtained results based on spectroscopic observations.
