  We investigate the dynamics of the nebula around the symbiotic star Hen
2-147, determine its expansion parallax, and compare it with the distance
obtained via the Period-Luminosity relation for its Mira variable. The geometry
of the nebula is found to be that of a knotty annulus of ionized gas inclined
to the plane of sky and expanding with a velocity of ~90 km/s. A
straightforward application of the expansion parallax method provides a
distance of 1.5+-0.4 kpc, which is a factor of two lower than the distance of
3.0+-0.4 kpc obtained from the Period-Luminosity relationship for the Mira
(which has a pulsation period of 373 days). The discrepancy is removed if,
instead of expanding matter, we are observing the expansion of a shock front in
the plane of the sky. This shock interpretation is further supported by the
broadening of the nebular emission lines.
