  It is common to attribute a flat rotation curve to our Galaxy. However
Galazutdinov et al. (2015) in a recent paper have obtained a Keplerian rotation
curve for interstellar clouds in outer parts of the Galaxy. They have
calculated the distances from equivalent widths of interstellar CaII lines. The
radial velocity was also measured on the interstellar CaII absorption line.
  We verify the result by Galazutdinov et al. (2015) basing on observations of
old open clusters. We propose, that the observations of flat and Keplerian
rotation curves may be caused by the assumption of circular orbits. The
application of formulas derived with the assumption of circular orbits to
elliptical ones may mimics the flat rotation curve. The interstellar clouds
with cross-sections larger than stars may have almost circular orbits, and the
derived rotation curve will be Keplerian.
