  Milli-arcsecond resolution Very Long Baseline Array (VLBA) observations of
the archetype WR+O star colliding-wind binary (CWB) system WR140 are presented
for 23 epochs between orbital phases 0.74 and 0.97. At 8.4 GHz, the emission in
the wind-collision region (WCR) is clearly resolved as a bow-shaped arc that
rotates as the orbit progresses. We interpret this rotation as due to the O
star moving from SE to approximately E of the WR star, which leads to solutions
for the orbit inclination of 122+/-5 deg, the longitude of the ascending node
of 353+/-3 deg, and an orbit semi-major axis of 9.0+/-0.5 mas. The distance to
WR140 is determined to be 1.85+/-0.16 kpc, which requires the O star to be a
supergiant. The inclination implies the mass of the WR and O star to be 20+/-4
and 54+/-10 solar masses respectively. We determine a wind-momentum ratio of
0.22, with an expected half-opening angle for the WCR of 63 deg, consistent
with 65+/-10 deg derived from the VLBA observations. Total flux measurements
from Very Large Array (VLA) observations show the radio emission from WR140 is
very closely the same from one orbit to the next, pointing strongly toward
emission, absorption and cooling mechanism(s) that are controlled largely by
the orbital motion. The synchrotron spectra evolve dramatically through the
orbital phases observed, exhibiting both optically thin and optically thick
emission. We discuss a number of absorption and cooling mechanisms that may
determine the evolution of the synchrotron spectrum with orbital phase.
