  The direction angle of twilight sky background polarization in the celestial
sphere points far from solar vertical is found to depend on the ratio of single
and multiple scattering contributions. The polarization direction behavior
during the twilight is related with general properties of background components
and can be used to check the accuracy of their separation method. The basic
assumptions of this method are confirmed by analysis made in this paper. This
helps to hold the temperature and scattering medium study in the upper
mesosphere, the least accessible layer of the Earth's atmosphere. The
mesosphere temperature data obtained during the observations from 2011 till
2014 are also presented.
