  The radio galaxy 0402+379 is believed to host a supermassive black hole
binary (SMBHB). The two compact core sources are separated by a projected
distance of 7.3 pc, making it the most (spatially) compact resolved SMBHB
known. We present new multi-frequency VLBI observations of 0402+379 at 5, 8, 15
and 22 GHz, and combine with previous observations spanning 12 years. A strong
frequency dependent core shift is evident, which we use to infer magnetic
fields near the jet base. After correcting for these shifts we detect
significant relative motion of the two cores at $\beta=v/c=0.0054 \pm 0.0003$
at $PA= -34.4^\circ$. With some assumptions about the orbit, we use this
measurement to constrain the orbital period $P\approx 3 \times 10^4$ y and
SMBHB mass $M \approx 15 \times 10^9\ M_\odot$. While additional observations
are needed to confirm this motion and obtain a precise orbit, this is
apparently the first black hole system resolved as a visual binary.
