  In this work we present an observational technique and a detailed analysis of
the stellar interferograms produced by three bright stars: Betelgeuse, Rigel
and Sirius. It is shown that the atmospheric turbulence is responsible for the
reduction of the long-exposure fringe visibility of the obtained interference
patterns. By using different baselines in our interferometer, we are able to
distinguish the decay of the visibility with the baseline, how different
parameters such us the diameter of the holes in our interferometer or their
distribution affects the pattern, and to measure the turbulence with the
estimation of the Fried parameter r0. The work and methodology are presented as
a method for postgraduate students that targets practical learning of optical
interferometry in astronomy and how it is affected by several causes, such as
the atmospheric turbulence.
