Tag: Callisto

As promised: Jupiter and moons seen by SOHO

By Phil Plait | May 17, 2012 1:56 pm

A little while back, I wrote about Jupiter appearing in an image from NASA’s SOHO Sun-observing satellite. I promised that it would soon appear in a SOHO camera that had higher magnification, and we’d be able to see its moons.

I am not one to break promises:

Awesome. It helps to set the resolution to 720p to see the moons when they’re pointed out.

And just you wait: in early June, Venus will appear in the LASCO C3 and C2 cameras, on its way for a date transiting the Sun for the last time in over a century. I’ll have more about that event in a few days… I promise!

Tip o’ the occulting bar to SungrazerComets on Twitter.

Related Posts:

- Jupiter, acting all superior
- Lovejoy lives!
- The Sun fries a comet and we got to watch
- The Galilean Revolution, 400 years later

CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures
MORE ABOUT: Callisto, Ganymede, Jupiter, SOHO, Sun

Saturn's biggest kids play peek-a-boo

By Phil Plait | July 1, 2011 11:30 am

I spent all day yesterday writing a 2000-word article for a print venue to be named later, and the weather outside is sunny and delightful and begging to be biked in, so I am disinclined to write something deep and philosophical today. So instead here is just a simply way-cool picture from Cassini taken in 2009, showing the Saturnian moon Rhea peeking out from behind the much larger Titan:

[Click to eneldergodenate.]

[UPDATE: I messed up here. In the original post I misread Titan's radius when I looked it up, and was comparing it to Rhea's diameter. This changes my numbers enough that I have simply corrected everything below; otherwise it would be too confusing to read. Thanks to the commenters for pointing this out!]

Rhea is a little over 1500 km (900 miles) across, and Titan 5150 km (3100 miles). However, in this shot, Rhea was almost two and a half times farther away than her big sister, so it looks smaller than it really is. Titan has a thick atmosphere, which is pretty obvious in the picture, while Rhea is basically a ginormous iceball.

Still, hmmm. Titan and Rhea are the two largest moons of Saturn, but to be honest Titan really is a lot bigger than Rhea, more than 3 times wider. Why such a big gap in sizes? Jupiter’s two largest moons, Ganymede and Callisto, are much closer together in size (5260 and 4820 km, respectively), and Ganymede is only 1.7 times bigger than Jupiter’s fourth largest moon, Europa. After that, though the rest are far smaller.

It seems to me that Saturn and Jupiter are telling us something about the physics of the way their moons formed. But what could it be? Titan orbits well over twice as far from Saturn as Rhea, while Ganymede is actually closer to Jupiter than Callisto. Is that important? Did those moons form at other distances and get their orbits jostled through gravitational interactions over billions of years, maybe even switching positions?

These are pretty basic questions, but it’s questions like these that lead to basic insights on how our solar system formed and changed as time went on.

And dangit! I guess I did get a little deep and philosophical here. Ah well, what can I say? Images like this are so pretty and so interesting to look at, they spark all kinds of thought processes in my head. And the more I do that, the more I want to do that. Science is like that: addictive, but in a good way.

Damn! Did it again.

Image Credit: NASA/JPL/Space Science Institute

Related posts:

- Cassini’s pentaverate
- Peeking past Rhea
- Dione and Rhea, sitting in a tree
- Titanic slice

The Galilean Revolution, 400 years later

By Phil Plait | January 7, 2010 10:00 am

Four hundred years ago tonight, a man from Pisa, Italy took a newly-made telescope with a magnifying power of 33X, pointed it at one of the brighter lights in the sky, and changed mankind forever.

The man, of course, was Galileo, and the light he observed on January 7, 1610 was Jupiter. He spotted "three fixed stars" that were invisible to the eye near the planet, and a fourth a few days later.

Here is how he drew this, 400 years ago:


He noted the stars moved around Jupiter as they followed it across the sky, and so was the first to figure out that other planets had moons like our own. It wasn’t an easy observation; his telescope was still small, the field of view narrow (so not all the moons were visible at the same time), and the moons faint next to Jupiter’s brilliant glare. But Galileo persisted, and figured it out. We call these four the Galilean moons in his honor: Io, Europa, Ganymede, and Callisto.

Here’s how we see them today:


The image above [click to embiggen] is from the New Horizons spacecraft as it shot past Jupiter in early 2007, showing all four moons. Each is scaled to show its true relative size to the others. It’s impossible not to wonder what Galileo would have thought, knowing that just shy of 400 years after he made his first observations, we would fling our robotic proxies out into the solar system and get close up views of the objects he discovered.

Think of it! For all of time before, Jupiter was just a light in the sky. And then, forever after that night forty decades ago, it was a world, surrounded by more worlds.

[See more pictures of Jupiter and its moons in a gallery over at 80 Beats.]

Galileo went on to observe craters on the Moon, spots on the Sun, and the phases of Venus. It was that last that may have been his crowning achievement, because the way Venus showed phases meant it could not possibly orbit the Earth, and that it must orbit the Sun. The geocentric theory had held sway for over a thousand years, but Galileo proved it was wrong almost overnight. Of course, the Church wasn’t thrilled with this, though I suspect they might have rolled with it if Galileo hadn’t been such an arrogant jerk and published a manuscript insulting the Pope, a man who used to be his friend and supporter.

If there is a lesson in there, I leave it to my readers to suss it out.

Now, all these years later, a lot of legends exist over the man. He didn’t invent the telescope, he wasn’t the first to point it at the sky, and he wasn’t even the first to publish his drawings. But he was a merciless self-promoter, and because of that we do remember him now (again, any lessons learned here are up to you). And it’s not entirely unfair to do so; he was a tireless observer, a wonderful artist, a great inventor (he may not have been the first to build a telescope, but he made his far better than its predecessors) and a brilliant scientist who, even if he hadn’t done so much for astronomy, would still be remembered today for his other work.

Tonight, just after sunset, Jupiter will be a glowing white beacon in the southwest. I have a Galileoscope, an inexpensive telescope created as part of the International Year of Astronomy 2009, an effort to get as many people on Earth to look up as possible. I think perhaps it would be fitting if I brave the subzero temperature outside, maybe for just a few minutes, and take a look at the mighty planet. Tonight’s display is better than Galileo himself had it: all four moons will be perfectly arrayed, two on each side of Jupiter’s face.

I’m not a very religious man, nor am I a very spiritual man. But I know there will still be a sense of connection, a sense of wonder that I will have tonight that I will share with a man long dead, but whose life and achievements still echo through time.

CATEGORIZED UNDER: Astronomy, Cool stuff, Science

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