Log, Jan 7, 2001
3 people. Tonight the shadows of Ganymede and Io crossed the face of Jupiter together forming a very visually interesting event. You can see the image at The double transit occurred while the Great Red Spot [GRS] was turned towards us. Joe and Les arrived at about 8 PM. Ganymede had already completed its own transit across the face of Jupiter about an hour and a half earlier. Neither shadow was on the surface of Jupiter. Barry arrived perhaps an hour later after he went in from his patio where he has been using his own telescope to find our e-mail invitation.At A (roughly 8 PM) Ganymede was near the "left" side of Jupiter in our mirror imaged view. Io was just to the "right". We watched as Io crept closer to Jupiter and finally created a "pimple: on the right limb. the GRS was already visible right of center on the planet's surface. While conditions were far from ideal, with thin to moderate clouds, a bright Moon nearby and cold/cool conditions, we were able to get really spectacular views in moments of good clarity using our Meade 16" SCT and Joe's new gift to FDO, a beautiful 19 mm eyepiece which produced images at around 215X.Actually, the worst thing that happened to us was the thermos of what Les thought was coffee. A ghastly brew it was - with a flavor best described as the Connecticut River Effluent at low tide. Les suspects that the thermos had some left over dishwater from its last cleaning.As the evening progressed first Ganymede's shadow and a little later Io's shadow passed over Jupiter. Io itself was normally lost since a pale yellow dot against a pale yellow background has almost no contrast. However, the shadow's very very distinct. We counted at least ten bands on the surface, with a great deal of definition in both tropical bands. Where the GRS touched the southern tropical band, the northern boundary of the GRS was white, with a darker band to the south. The GRS looked a bit like someone's eye.Ganymede moves at almost exactly a quarter the rate of Io. Even so, because it's shadow was lower on Jupiter and because it started first, it exited Jupiter first after 11 PM. A bit later Io itself emerged from the surface of Jupiter. We decided not to wait for the final event [Io's shadow exiting]. It was rather interesting that Ganymede's shadow was leaving Jupiter just as Io face was passing off Jupiter. The two looked rather like negatives of each other.-Les Coleman
