  Following previous investigations by Giordano and Mancuso [1] and Mancuso and
Giordano [2, 3] on the differential rotation of the solar corona as obtained
through the analysis of the intensity time series of the O VI 1032 Ang.
spectral line observed by the UVCS/SOHO telescope during solar cycle 23, we
analysed the possible influence of projection effects of extended coronal
structures on the observed differential rotation rate in the ultraviolet
corona. Through a simple geometrical model, we found that, especially at higher
latitudes, the differential rotation may be less rigid than observed, since
features at higher latitudes could be actually linked to much lower coronal
structures due to projection effects. At solar maximum, the latitudinal
rigidity of the UV corona, with respect to the differential rotating
photosphere, has thus to be considered as an upper limit of the possible
rigidity. At solar minimum and near the equatorial region throughout the solar
cycle, projection effects are negligible.
