  The influence of rotating binary systems on the light curves of galactic
microlensing events is studied. Three different rotating binary systems are
discussed: a rotating binary lens, a rotating binary source, and the motion of
the earth around the sun (parallax effect). The most dramatic effects arise
from the motion of a binary lens because of the changes of the caustic
structure with time. I discuss when the treatment of a microlensing event with
a static binary model is appropriate. It is shown that additional constraints
on the unknown physical quantities of the lens system arise from a fit with a
rotating binary lens as well as from the earth-around-sun motion. For the DUO#2
event, a fit with a rotating binary lens is presented.
