Wednesday, May 02, 2007

Galileo's Moons

Io and Europa in the same frame March 2, 2007, two days after New Horizon's flyby of Jupiter. As the spacecraft sped away it took this long-lens photo. The moons are in fact separated by 790,000 kilometres. Eruption of the volcano Tvashtar is still very visible. Io's night side is lit by Jupiter, a planet which gives off twice as much radiation as it receives from the Sun. Europa's night side is dark because it is on the other side of Jupiter.

The night of January 7, 1610 Galileo first noticed strange objects around Jupiter. By January 13 he had seen 4 moons. Discovery of new worlds was truly exciting and kept Galileo up every night. By March 22 he had finished his observations, and immediately started writing his observations in book form.

STARRY MESSENGER was published that same year and was immediately popular. The book was also controversial, because not everyone believed in the new moons. Someone named Horky, who had been a student of Johannes Kepler, wrote a book claiming that the moons were a fraud designed to gain fame and wealth. Kepler was very unhappy, but he counseled Galileo not to respond to such attacks.

Pictured to scale by New Horizons are Io, Europa, Ganymede and Callisto. The moons will be there long after the doubters are underground. Kepler's advice to Galileo was right on.

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Anonymous Anonymous said...

Hi Louise,

great post - and great picture! Especially nice is that by looking at the pic one understands at once where Jupiter is and where the moons are with respect to it.

By the way, I have always hoped to see a phemu... Phemus are mutual effects when one of the satellites eclipses, occults, or transits another. Seeing these pictures taken from probes that can have whatever point of view I feel betrayed, since I am stuck here and have to wait ten years, while these wonderful pics arrive!


10:57 AM  
Blogger Fraser Cain said...

That's a great choice of photos from the bunch released by New Horizons. And just think, we're only looking at the appetizer. I can't wait until the spacecraft gets to Pluto.

Fraser Cain - Astronomy Cast/Universe Today

11:39 AM  
Blogger CarlBrannen said...

The observations of these moons gave clues as to what is conserved in gravitation. From those conserved quantities, Newton deduced the gravitational potential. Thus began a long tradition of physicists using observed symmetries to guess the equations of nature.

However, if Newton had begun by guessing simple potential functions, he'd likely have finished his work sooner.

Nature seems to arrange for the equations of motion to be simpler than the conserved quantities. This suggests that maybe we should get away from thinking of physics as a search for symmetries, and instead see it as a search for equations of motion.

7:10 PM  
Blogger L. Riofrio said...

Great hearing from you Tommaso. There will be news soon on something getting published.

A great honour hearing from you, Fraser. I link and read UT every day. Hopefully 2015 will come soon! At the end of the month there will be separate news of great interest to human spaceflight.

Carl, that sounds like a good idea. It would explain why so many physicists have gone off the tracks searching for symnetries, supersymnetry...etc.

7:22 PM  
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4:35 AM  
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8:13 PM  

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