Here’s a photo-op pretty enough to tempt any astronomer. With a series of well-timed shots, NASA’s Hubble Space Telescope has managed to catch three of Jupiter’s biggest moons whizzing across its surface in the same frame.
This Jovian lunar gathering, which took place Jan. 24, is a relatively rare event — it happens only once or twice a decade. Hubble had to snap a series of images in fairly quick succession to capture the brief moment when all three could be seen hovering over the colorfully banded planet.
The three moons, Europa, Callisto and Io, are three of the four Galilean satellites — so named because astronomer Galileo Galilei discovered them in 1610. (The largest, Ganymede, was off-screen and too far to be considered part of the conjunction.) These four moons are Jupiter’s largest, and among the largest bodies in the solar system.
To put that in perspective: these four moons are bigger than all the dwarf planets, Pluto and Ceres included. Three of them (Ganymede, Callisto and Io) are all larger than Earth’s moon, and Ganymede is larger than the planet Mercury.
In this image, the Jovian moons are traveling from the bottom left toward the top right as they cross Jupiter’s midriff, and their shadows are cast far in front of them; near the beginning of conjunction, Callisto’s shadow looks like it’s almost directly beneath Io.
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SOURCE: LA Times, Amina Khan