Tuesday, November 30, 2004

Jupiter's moons

Here's a puzzle for you, a recent Hubble Space Telescope photograph of Jupiter. The three black dots are the shadows of three of Jupiter's moons, in a rare triple solar eclipse: Io, Ganymede and Callisto (listed in order of their distance from the planet). Two moons are visible: Ganymede is the blue dot, and Io is the white dot just slightly above the planet's center.

Can you match shadows to moons? Where in the sky relative to the photograph would you go looking for Callisto? (Answer tomorrow.)

Although Io and Ganymede (the white and blue dots) look like they are swimming in Jupiter's clouds, they are actually well in front of the planet, Io by about 2.5 Jupiter diameters, and Ganymede by 14 diameters.