DOLPHOT's estimate of the local sky for a sequence of exposures taken during a single orbit visit for UGC4305-1, based on DOLPHOT's PSF fitting. The first exposure in the orbit is in the upper left, and the final exposure is in the lower right. Exposures alternate between F110 W and F160 W, and all images for a single filter have been displayed with a common scale and stretch. There is an overall gradient from top to bottom in all images, due to a larger fraction of unresolved sources in the upper half of the image. There is also a time-dependent feature on the left-hand side of the image, due to scattered light. We show in Figure 5 that this feature appears when the telescope is pointed to within 30° of a bright Earth limb; the first two exposures in the orbit had average limb angles of 22° and 26°, respectively, while the third through sixth exposures have limb angles of 31°, 34°, 36°, and 37°, respectively. Even after the bright limb feature disappears, there are still temporal variations in the overall sky brightness level.