As Cassini weaves its way around the multiple moons of Saturn, it’s not really a coincidence when one gets in the way of another. As a matter of fact, it’s a guarantee. These are called mutual events, and when Cassini dove past Dione, it saw this terrific view of Mimas peeking out from behind it:

Nifty, huh? [Click to encronosenate.]

Dione is nearly 3 times larger than Mimas (1100 versus 400 km wide), but Mimas was also more than 6 times farther away, making Dione loom nearly 20 times larger in this shot. I like how you can’t really see the unlit side of Dione, but Mimas marks it pretty well, sliced in half by the edge of the larger moon.

Funny, too: I was thinking to myself that if Cassini was in position to catch this shot, then it should have also caught Mimas when it was on the other side of Dione, the lit part. Well, seek and ye shall find: I searched the Cassini raw image archive and found it! I put a small version of it here; click to embiggen. You can just barely see a small segment of Saturn’s rings in the lower left corner, too.

Neat! I like it when stuff makes sense. While this alignment is rare to see from Earth — we’re a lot farther away, and the geometry has to be precise — we do see moons transiting across their parent planets, and, far less often moons in front of moons. But what’s rare to us is common to Cassini, with its front row seat to this amazing system of worlds.

I know I’ve been writing about the Sun quite a bit lately, but I have a followup to yesterday’s cool video of the big solar flare… and you’re gonna like it.

I was fooling around with helioviewer.org, watching the flare in different wavelengths of light detected by NASA’s Solar Dynamics observatory, when I switched to 17.1 nanometers — in the far ultraviolet. At that wavelength, the glowing plasma that flows along the Sun’s magnetic field lines is very bright. The images were so beautiful, so incredible, I made a video animation of them, covering the time range of January 26, 2012 at midnight to January 28 at noon (UTC), which includes the huge X2 solar flare that erupted on the 27th. The video shows huge loops of magnetism on the Sun’s surface, glowing plasma flowing along them… and then 48 seconds in the flare changes everything. Watch:

Holy wow! Isn’t that awesome? Make sure you watch in in HD, and make it full screen to get the whole effect.

What you’re seeing is Active Region 1402, a sunspot cluster. This is a tangled collection of magnetic field lines piercing the surface of the Sun. Like a bar magnet, there are two poles to each loop, a north and a south pole. The gas on the surface of the Sun is so hot it has electrons stripped off, so it’s strongly affected by the intense magnetic field, and flows along these towering loops, which can reach heights of 300,000 km (180,000 miles) in this region.

The loops are tied to the plasma, too, and this material is twisting and roiling as it rises and sinks. The lines get tangled, and like a short circuit they can snap and reconnect. When they do, they release vast amounts of energy as a solar flare. In the video you can see the messy, disorganized loops getting more and more tangled up. Then KABLAM! The flare itself is not visible because it happened too quickly to be seen on this timescale (see the video yesterday for that). But you can see the effect on the magnetic field loops! They suddenly become far more organized, tight, and calm.

The Sun is fiendishly complex, and astonishingly beautiful. Clearly, to our brains, these things are connected. Remember, too: this beauty, this magnificence, is brought to you by science. Without our curiosity and our need to understand the Universe better, you would never have been able to watch in awe as superheated plasma arcs dwarfing the Earth itself grew and collapsed on the surface of a star one hundred fifty million kilometers away.

Think of that the next time someone says science takes away the beauty and mystery of life.

Credit: NASA/SDO/Helioviewer.org

Photographer Alistair Chapman traveled to Tromso, Norway — 300 km north of the Arctic Circle — to capture video of the aurorae from the recent spate of solar storms. What he caught on camera is remarkable: shimmering, waving, dancing lights moving in real time!

[Make sure you set it to 720p; Chapman says higher-def footage is coming soon.]

That’s amazing. Aurorae video is generally done with time lapse to show the movement, which is usually slow. I’ve often wondered just how fast the movement really is; I always figured fluctuations in the solar particle density, speed, and magnetic fields would produce real-time changes in the lights, but I’d never seen anything like this! After a search of YouTube I actually found several more.

I know some people will think this is fake, and I had my skeptic hat on while watching it. Note that in most time lapse you can see the stars move; in this they don’t, indicating (unless it’s a complete fake) short periods of time during the filming. Given that, plus the existence of other video like it, I’m thinking this is real.

Mind you, the movement you’re seeing isn’t a physical motion. It’s not like solid curtains of material are flapping. The lights are caused by atoms in the upper atmosphere getting hit by subatomic particles blasted out by the Sun, caught by our Earth’s magnetic field, and funneled down into our air. These particles dump energy into the atoms, moving the electrons up in energy (called excitation). The electrons then jump back down, emitting light in the process (de-excitation). As I said in an earlier post, it’s like needing energy to jump up stairs, but releasing it as you jump down.

Different atoms have different energy levels for the electrons — think of it as more or less spacing vertically between steps in a staircase — so the energy emitted is different, resulting in different colors emitted. That’s why we see green, red, purple… they come mostly from oxygen and nitrogen in the air. So as the magnetic field fluctuates, the particles are sent shooting down in different places, giving the appearance of motion while the atoms themselves don’t move.

The physics is complex and interesting, but the beauty of these lights is, to use another term, magical. Not in the fantasy sense, but in the sense of the emotional response we have to them. They are simply breathtaking in these videos, and are a wonderful by-product of our tempestuous Sun.

Tip o’ the lens cap to sunspotter.

If you live nearly anywhere on Earth — those of you north of 73° you’re out of luck, but I’m guessing there aren’t many of you! — and look to the southeast shortly after sunset, you’ll see the figure of Orion. Follow the three belt stars to the east, and you’ll see a bright star: Sirius, the brightest star in the night sky. If it’s near the horizon, you may see it twinkling madly: flickering, dancing, perhaps even changing color.

This gave astronomer David Lynch an idea: take a time exposure of Sirius with a camera and telephoto, and purposely wiggle the mount. He tried it on January 4, 2012, and the result he got is actually quite lovely:

Isn’t that cool? As the vibrating camera caused the star to trail around, the changing colors got recorded along the track. The changing brightness of Sirius can be seen as well, as parts of the loop-de-loop fade and intensify.

The reason stars twinkle is because of our atmosphere: little blobs of air are constantly in motion. These air parcels act like lenses, and as light passes through them, the path of the ray gets bent a little bit. That’s what causes the dancing motion, the actual twinkling. Different colors get bent by different amounts (which is why prisms break up white light into separate colors).

While it’s beautiful to our eyes, twinkling is a major pain to astronomers. It blurs our images! That’s why we launch telescopes into space, or design fancy optics for ground-based telescopes to remove it. Twinkling is free, but correcting it sure ain’t.

Lynch has several websites loaded with interesting pictures he’s taken of nature, including Thule Scientific, Color and Light in Nature, and San Andreas Fault.

Image credit: David Lynch (used by permssion). Tip o’ the Snell’s Law to Earth Science Picture of the Day.

In 2007, the European Space Agency probe passed by Mars on its way to visit a comet. It used Mars for a gravity assist to help it on its way, and got close enough to take some very detailed pictures (it also passed by the asteroid Lutetia and returned amazing shots; see the gallery at the bottom of this post). That data wasn’t initially released by the mission leader (that’s fairly common in some missions), but they were finally made available late last year. My pal Emily Lakdawalla from the Planetary Society Blog grabbed a bunch of them and put together some simply amazing pictures from them, including this jaw-dropper:

Yeah. You really want to click that to Barsoomenate it. Holy dry ice polar caps!

In fact, you should go over to her blog where she gives all the details and has more incredibly cool pictures of the Red Planet as well. I don’t want to spoil her fun by giving it all away here. Go!

Credit: ESA / MPS / UPD / LAM / IAA / RSSD / INTA / UPM / DASP / IDA / processed by Emily Lakdawalla

- Rosetta’s cometary goal now in sight
- Lutetia may have witnessed the birth of the Earth
- Curiosity on its way to Mars!

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The solar storm that impacted Earth Tuesday produced a lot of auroral activity, though it’s hard to say if it was really that much stronger than usual. Still, any aurora is better than none… and I have two videos to show you!

The first was taken on January 22, and shows the effects of an earlier wave of subatomic particles spat out by the Sun. It was made in Birtavarre, Norway by Ørjan Bertelsen, who put together 1600 exposures to make it:

It’s amazing to get the three-dimensional effect as the sheets of glowing atmospheric molecules pass overhead, and you’re seeing them nearly edge-on. And I love picking out familiar constellations in videos like that; did you see Leo, Gemini, Cancer, and Taurus?

The second video was shot in Abisko National Park, Sweden, by Chad Blakley, and all I can think of as I watch it is how cold those people must have been!

As I mentioned in a radio interview on Tuesday, I’ve never seen a bright aurora. Once in Maryland I saw a reddish glow to the extreme north during a particularly big display, but that’s really about it. Someday, though, I’ll get a chance. As the Sun gets more active over the next two years I may very well finally see these magnificent light shows. After writing about them so much, I think I’ve earned it.

Tip o’ the parka hood to John Markus Bjørndalen.

Just before Halloween last year, NASA launched into orbit the improbably named National Polar-orbiting Operational Environmental Satellite System Preparatory Project, which they thankfully shortened to NPP. In its low 800 km (500 mile) orbit it looks down at the Earth to investigate our environment. It only sees a portion of the Earth at any one time, but if you take observations taken during a single day — say, on January 4, 2012 — and stitch them all together, you get this magnificent shot:

[Click to engaiaenate, or download the Big McLarge Huge 8000 x 8000 pixel version.]

Man, the resolution is so high is like you’re actually there.

Oh wait.

In fact, the biggest version is 8000 pixels across, and the Earth is about 8000 miles wide, so the resolution is about a mile per pixel. We’re not seeing the entire hemisphere here, but the view is roughly 8000 km across (judging from the size of the US compared to the view). The big image is 8000 pixels wide, so the resolution of that mosaic is about 1 km/pixel. The Earth is big.

NPP was recently renamed Suomi NPP in honor of Verner Suomi, a pioneer in using satellites in meteorology. I like that we tend to name satellites and space probes after people whose work made those very missions possible, or for people we honor and respect (my favorite is still Sojourner, the Mars rover named after Sojourner Truth… with the bonus of the name being a pun).

Apropos of nothing, I’ll note the images making up this seamless mosaic were taken around the same time the Earth was at perihelion, when it was closest to the Sun in its orbit. There is nothing particularly important about that fact, but still… when I see pictures like this I think about how amazing our planet is, and how wonderfully well-adapted we are to it. Evolution is a stochastic process, a semi-random series of bumps and false starts that literally made us who were are today. But that doesn’t change the feeling of comfort I get when I see a picture of Earth, floating in space, sitting in the brightest and warmest sunlight of the year.

It’s home, and I’m glad we’re taking such a close look at it.