Free Astronomy Magazine March-April 2015

SPACE CHRONICLES Hubble captures rare triple moon transit of Jupiter by NASA T he image on the left shows the Hubble ob- servation at the begin- ning of the event. On the left is the moon Callisto and on the right, Io. The shadows from Europa, which cannot be seen in the image, Callisto, and Io are strung out from left to right. The image on the right shows the end of the event, approxi- mately 42 minutes later. Europa has entered the frame at lower left with slower moving Callisto above and to the right of it. Meanwhile Io — which orbits significantly closer to Jupiter and so appears to move much more quick- ly — is approaching the eastern limb of the plan- et. Whilst Callisto’s shad- ow seems hardly to have moved Io’s has set over the planet’s eastern edge and Europa’s has risen further in the west. The movement of the moons is shown in the video created from Hubble stills. [NASA, ESA, Hub- ble Heritage Team] T hese new NASA/ESA Hubble Space Telescope images capture a rare oc- currence as three of Jupiter’s largest moons parade across the giant gas planet’s banded face. Hubble took a string of im- ages of the event which show the three satellites — Europa, Callisto and Io — in action. There are four Galilean satellites — named after the 17 th century scien- tist Galileo Galilei who discovered them