THE EXPANSION RATE OF AND DISTANCE TO G5.89-0.39

The expansion rate of the ionized shell in the ultracompact H II regio n G5.89-0.39 has been measured using three VLA observations spanning 5 .3 yr. The nebular shell is expanding at a rate of 2.5 +/- 0.5 mas yr( -1). From the angular radius and expansion rate, we find a dynamical a ge of 600(-125)(+250) yr. Combined with a model for the nebular emissi on and H radio recombination line spectra, we estimate an expansion ve locity of about 35 km s(-1) and a source distance of 2.0(-0.4)(+0.7) k pc. This is slightly closer than most previous estimates of 2.5-3 kpc. We see no evidence for northeast-southwest expansion that might be as sociated with the molecular outflow seen in SiO; however, our data are consistent with previous observations of a north-south how, indicatin g that the SiO flow may originate from another young star along the li ne of sight.