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This paper reports dual-epoch, Very Long Baseline Array observations of H Iabsorption toward 3C 147. One of these epochs (2005) represents newobservations while one (1998) represents the reprocessing of previousobservations to obtain higher signal-to-noise results. Significant H I opacityand column density variations, both spatially and temporally, are observed withtypical variations at the level of \Delta\tau ~ 0.20 and in some cases as largeas \Delta\tau ~ 0.70, corresponding to column density fluctuations of order 5 x10^{19} cm^{-2} for an assumed 50 K spin temperature. The typical angular scaleis 15 mas; while the distance to the absorbing gas is highly uncertain, theequivalent linear scale is likely to be about 10 AU. Approximately 10% of theface of the source is covered by these opacity variations, probably implying avolume filling factor for the small-scale absorbing gas of no more than about1%. Comparing our results with earlier results toward 3C 138 (Brogan et al.),we find numerous similarities, and we conclude that small-scale absorbing gasis a ubiquitous phenomenon, albeit with a low probability of intercept on anygiven line of sight. Further, we compare the volumes sampled by the line ofsight through the Galaxy between our two epochs and conclude that, on the basisof the motion of the Sun alone, these two volumes are likely to besubstantially different. In order to place more significant constraints on thevarious models for the origin of these small-scale structures, more frequentsampling is required in any future observations.

Spatial Variations in Galactic H I Structure on AU-Scales Toward 3C 147 Observed with the Very Long Baseline Array