  Measurements of cosmic neutrinos have a reach potential for providing an
insight into fundamental neutrino properties. For this a precise knowledge
about an astrophysical environment of cosmic neutrinos propagation is needed.
However this is not always possible, and the lack of information can bring
about theoretical uncertainties in our physical interpretation of the results
of experiments on cosmic neutrino fluxes. We formulate an approach that allows
one to quantify the uncertainties using the apparatus of quantum measurement
theory. We consider high-energy Dirac neutrinos emitted by some distant source
and propagating towards the earth in the interstellar space. It is supposed
that neutrinos can meet on their way to the detector at the earth a dense
cosmic object serving as a filter that stops active, left-handed neutrinos and
letting only sterile, right-handed neutrinos to propagate further. Such a
filter mimics the strongest effect on the neutrino flux that can be induced by
the cosmic object and that can be missed in the theoretical interpretation of
the lab measurements due to the insufficient information about the
astrophysical environment of the neutrino propagation. Treating the neutrino
interaction with the cosmic object as the first, neutrino-spin measurement,
whose result is not recorded, we study its invasive effect on the second,
neutrino-flavor measurement in the lab.
