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G. Schneider (Steward Observatory, University of Arizona), J.M. Pasachoff (Willimas College, Hopkins Observatory), L. Golub (Smithsonian Astrophysical Observatory)
We present time-resolved (38s) high-resolution (500mas) imagery of the ingress phase of the 15 November 1999 transit of Mercury observed with the Transition Region Coronal Explorer (TRACE) spacecraft in its "white light" (1600 - 6000 Angstrom) channel. As part of our photometric and astrometic analyses of this data set we examined the images in and around the point of internal tangency for evidence of the historical "black drop effect". After calibration (including careful removal of image/instrumental artifacts and flat-fielding) the only radially directed brightness anisotropes found were due to the interacting effects the back-light solar limb-darkening, diffraction of photospheric light around the Mercurian disk, and the instrument's Point Spread Function. We discuss, and model, these effects as they would have applied to earlier ground-based observations of Mercurian transits (also including the effects of atmospheric "seeing") to explain the historical basis for the black drop effect.