Figure 1: STIS image (raw data). The second, fourth, and sixth images, which are less contaminated with terrestrial airglow than the others, have been combined to reduce noise. Each image is 1024 × 1024 pixels, each 0.0244´´ square on the sky plane, with 0.584 Å/pixel dispersion convolved with the spatial information horizontally; thus, for each emission wavelength, a "slit image" appears at a different (but potentially overlapping) position on the detector. Positions of slit images for expected emission wavelengths are shown above the image. The circular features are emission near Io's limb.