400 Years After Galileo Spotted Them, the Moons of Jupiter Are Looking Fly

By Eliza Strickland | January 7, 2010 11:24 am

1-all-moonsOn January 7, 1610, Galileo Galilei pointed his “spyglass” to the heavens and stared up at Jupiter, one of the brightest lights in the evening sky, and noted what he at first assumed to be three bright stars near the planet. But over the following nights, he realized that those three bright bodies weren’t fixed in the heavens like stars, but rather seemed to dance around Jupiter along with a fourth, smaller body.

Galileo triumphantly announced his discovery of four “planets” that revolved around Jupiter in his March treatise, Starry Messenger [pdf]. Thinking of his pocketbook, he dutifully proposed naming them the Medicean Stars in honor of his patron, Cosimo de Medici. But the name didn’t stick, and today we honor the scientist rather than the patron by calling Jupiter’s four largest satellites the Galilean moons.

The discovery dealt a death blow to the Ptolemaic understanding of the universe, in which all planets and stars were believed to orbit the Earth. For, as Galileo wrote in his treatise, “our own eyes show us four stars which wander around Jupiter as does the moon around the earth.”

In the 400 years that have passed since Galileo first laid eyes on them, we’ve learned a great deal about the moons Io, Europa, Ganymede, and Callisto (all named after the mythological paramours of Jupiter). If all goes according to plan we’ll soon get to know them much more intimately–NASA and the European Space Agency are currently planning missions to closely observe three of the moons. Click though this gallery to view NASA’s most stunning photos of the four satellites, and to find out what we’ve discovered in the four centuries since Galileo began the work.

(For more on Galileo’s discovery and what it meant to science, check out this post from DISCOVER’s Phil Plait.)


CATEGORIZED UNDER: Feature, Photo Gallery, Space
  • Michael Ullman

    What beautiful photos…..

  • Chester Knarl

    Europa is one of the most interesting places in the solar system…

    There is a prophetic warning about Europa. Heed it and attempt no landings there.

  • AJ

    what garbage is Chester Knarl saying? I think we should make Europa our next target for probes! Its very promising….

  • Kassul

    @AJ – Chester Knarl is referencing the book 2010 – A Space Oddessy, a not obscure book(especially to astronomy/science nerds) by Arthur C Clarke.


    The book is well worth a read, I’d encourage you to do so(as well as a number of other Clarke books, 2001 obviously being another.)

  • http://johntantalo.com John Tantalo

    “Its has an ice layer” should be “It has an ice layer” on page 4: http://emend.appspot.com/sites/blogs.discovermagazine.com/edits/3

    You also have a couple other typos I’ve spotted: http://emend.appspot.com/sites/blogs.discovermagazine.com/open

  • http://blogs.discovermagazine.com/80beats/ Eliza Strickland

    Thanks for the catch, John, I fixed the typo in this gallery.

  • http://www.carolcstrickland.com cacs

    These images put our own lovely moon to shame — I used to think cratered silver was the ultimate satellite attire, but now I see how flamboyant celestial bodies can be. And imagine volcanoes erupting on Io for decades! And Callisto’s crisscrossing bands and dots of light! The wonderment of it all. And while I’m wondering, would it be too much to ask of the universe for a moon that’s not a sphere? With all the possible shapes, you’d think somewhere we’d see a trapezoid or geodesic or something different. After all, we’re talking infinity here.

  • http://www.abidemiracles.com Emily Cragg

    Too hue-saturated for these spheres to reveal their transparent nature. Tone hue sat down about 50%. And of course, these moons are already populated except for IO.

    : )

  • Vic

    Launch date to Europa is 2020 but no lander due to lack of money?! How much money is the EU wasting on Africa over the next 10 years? Take that money and let’s put a lander and drill platform down on Europa. Good Lord!

  • http://www.pacificvacuum.com The Carpet Cleaner

    Ah, Galileo. I bow to thee…

    Absolutely wicked photos, very cool.

  • http://www.carpet-cleaning-equipment.net/jondon.shtml JonDon

    our moon does look pretty ugly by comparison to some of these

    deff no place to build a vactation home



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