[My Desktop Project -- clearing off the cool astropix from my computer's desktop by posting one each day -- is getting close to being done soon; I'm down to my last few pictures!]
It’s funny how different the Sun looks at different wavelengths of light. In visible light, you can see all sorts of surface features like sunspots, granules (rising and falling packets of gas convecting like a pot of water on a stovetop), and more.
But when you have eyes sensitive to the ultraviolet, the Sun takes on an entirely new appearance. That’s where the effects of the Sun’s active and crazy magnetic field claim dominion, and you see vast arcs, loops, and towers of incredibly hot plasma. To be fair, you can see this in visible light too, but it’s not quite so… dynamic. Cue NASA’s Solar Dynamics Observatory, and its UV detectors:
This image was taken by SDO on March 28, 2012, and shows the limb of the Sun at a wavelength of 19.3 nanometers — well into the UV. What you’re seeing is plasma — gas so energetic it’s had electrons ripped right off its atoms, putting it under the sway of the Sun’s fierce magnetism. The plasma flows along the magnetic field lines, arcing high off the surface into space before coming back down.
Usually, those arcs are hot and bright, like the tight loops you can see on the left (within hours, those loops got bigger and brighter, making dozens of well-defined glowing coils). But you can also see a dark arc in the center, going from just below the center of this picture, curving to the upper left, then heading up and over to the right, off the face of the Sun. For some reason, the plasma there wasn’t quite as hot, and so instead of glowing at this wavelength it appears dark, absorbing the light from material behind it.
I took this shot using Helioviewer.org — if you click the picture it will take you there. You can then play with the controls on the left and watch this dark filament change, grow, dance, and playfully flow from one arc base to the other. It’s mesmerizing. SDO has a page with some pre-made animations, too.
I love how we see the Sun pretty much every day, but in many ways it is as unfamiliar as any distant star. Happily, though, our drive to explore and understand has led us to the point where we can investigate our nearest star, and learn more about it. Given that it’s the main driver of life on Earth, this is probably a smart idea.
Image credit: NASA/SDO/Helioviewer.org
When you build and launch a high-resolution solar observatory that stares at the Sun 24 hours a day, you’re bound to catch some pretty cool stuff. As proof, check out this video of a stunning prominence erupting from the Sun’s surface on July 12, 2011, as seen by NASA’s Solar Dynamics Observatory:
[Make sure you set the resolution to at least 720p.]
That’s really graceful, especially considering that tower reached the staggering height of about 150,000 km (90,000 miles) above the Sun in just a few minutes!
The gas on the Sun is ionized, which means it’s had one or more electrons ripped away from its atoms. Technically called a plasma, this makes it sensitive to the Sun’s strong magnetic forces. That becomes really obvious after it starts to collapse; it doesn’t follow a ballistic trajectory like you’d expect (the path a ball thrown up in the air would follow), but instead flows along the Sun’s magnetic field lines. This video is in the ultraviolet, where such a plasma glows brightly.
For a moment there, just at its peak, it coincidentally looks like a classic angel with wings spread. Of course, once the angel dissolves it forms more of an arc… so I guess this makes it an archangel. I’m glad no one heard a trumpet playing when this happened. That could’ve been awkward.
It’s a little early for me to start thinking about my annual Top Ten Astronomy Pictures, but I have a feeling this one will make the cut: the actual glowing trail of plasma left in the wake of Atlantis as it entered Earth’s atmosphere, as seen from space by astronauts aboard the space station!
Amazing! Oh yes, you want to click to embiggen.
Atlantis undocked from the International Space Station on July 19, and two days later the ISS was in position to coincidentally catch a view of the Orbiter as it made its final descent. This shot shows the plume of ionized gas left behind as Atlantis descended, as well as clouds, parts of the ISS itself, and atmospheric airglow: the faint glow of molecules and atoms high in the atmosphere as they slowly recombine with electrons and emit light.
This shot is simply spectacular. Since the stars aren’t trailed, this must be a fairly short exposure, not more than a few seconds. The trail you’re seeing is therefore not actually the Orbiter streaking across the Earth! The plasma trail behind it fades with time, so the trail is brightest near the Orbiter’s position and fainter as you backtrack along its path. Think of it as an afterglow of the passing of Atlantis.
Why does this happen? The air gets heated by the Orbiter’s ramming the atmosphere at 20+ times the speed of sound. And contrary to popular belief, it’s not friction that heats the air, but compression. When you compress a gas it heats up (like when a bicycle pump gets hot when you use it a lot), and the Orbiter is screaming through the atmosphere at hypersonic speeds. That compresses the air a lot. A shock wave forms in front of the Orbiter, and the air begins to glow as it gets heated up to temperatures as high as 1260° C (2300° F).
That’s what you’re seeing above: the shocked, rammed, and glowing air as Atlantis pounded through it at several kilometers per second. And it did this many, many times over its life… until this one final time, caught on camera by astronauts high above the Earth.