[S II] 6731Å emission from the east ansa of the Io plamsa torus on December 3, 1988, at 6:36 UT. The part inside the blue circle is the actual image I got through the telescope (the McMath-Pierce solar telescope at Kitt Peak), consisting of light given off by ionized sulfur; the positions of Jupiter (red circle), Io (yellow dot), and Io's orbit (yellow ellipse) were calculated and added into the image later. The plasma, being electrically charged, is bound to Jupiter's magnetic field, which, like the Earth's, is not quite aligned with its spin; this is why the torus does not "line up" with Io's orbit. [This image is from my dissertation and is copyright © 1992 R. Carey Woodward, Jr.]