After I posted the video of the solar eruption earlier this week, I got a lot of questions about why material fell back from the explosion onto the Sun. The quick answer: gravity! A lot of the material from a prominence like that falls back onto the Sun because of the Sun’s strong gravity. Since the material is an ionized plasma – a gas stripped of one or more electrons — it follows the magnetic field lines of the Sun, so you can see graceful arcs of this stuff falling back down after the blast (see Related Posts below for links to more detailed descriptions of this phenomenon).
Oh, why describe it when I can show you? This video is from the NASA/JAXA Hinode spacecraft which observes X-rays from the Sun. It caught the event in loving detail:
See? Gravity does the work, but magnetism does the steering.
Tip o’ the phased plasma rifle in the 40 Watt range to Camilla Corona SDO.
Today, the Sun had two relatively minor — but quite cool-looking — events. One was a prominence eruption, where a loop of ionized gas is lifted from the Sun’s surface and is ejected into space, and the other an M1 class flare on the Sun’s edge. Neither will affect us here on Earth, but are interesting to watch.
The sunspot region that blew off that small flare is on the edge of the Sun rotating toward us right now, so if they continue to be active, we might see some fun flares and aurorae from them. Stay tuned!
The numbers on the side are wavelengths — in this case, 171 and 131 Angstroms, way out in the ultraviolet where violent magnetic events are more easily seen.
This flare was very powerful, and blasted out a wave of particles that’s expected to hit Earth sometime tonight after midnight EST (the exact time is difficult to determine). We’ll be OK down here on Earth, but there may be sporadic communication issues, power outages (maybe), and aurorae. If you’re on Google+, Camilla Corona SDO is the person to follow. She has updates and great links!
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 ...
Active Region 1402, the same sunspot cluster that blew out a solar flare and caused all the ruckus last week, is still being feisty: just before rotating to the other side of the Sun, it erupted in an intense, pulsing solar flare that actually was much more powerful than the one that happened last Monday. This was an X2 class flare, making it more than twice as energetic as Monday’s.
Happily, the flares were on the edge of the Sun’s disk, so the bulk of the radiation was aimed away from the Earth, but it still makes for some pretty dramatic footage. Using helioviewer.org I created a video showing about 2.3 hours of the Sun as seen by NASA’s Solar Dynamics Observatory. It shows the Sun in the extreme ultraviolet (at a wavelength of 19.3 nanometers if you wanna get geeky), where magnetic activity is seen easily. Watch the upper right corner of our friendly star… and make sure you make it HD and full screen.
Isn’t that awesome? The flare got so bright the automatic software dimmed the rest of the Sun to compensate, giving you an idea of just how powerful ...
The solar storm that erupted from the Sun yesterday reached the Earth today at about 15:00 UTC (10:00 a.m. Eastern US time). The wave of subatomic particles has been impacting the Earth’s magnetic field, and we’re starting to see some auroral activity:
Isn’t that lovely? That was taken at 18:00 UTC today from a webcam in Abisko, Sweden. Can you see the handle of the Big Dipper right below the green curtain? [More aurora webcam sites are listed below.]
The two biggest questions I’m getting on Twitter and Google+ are 1) is there any danger to this storm, and b) can I see the aurora from [my location]?
First, no, we’re not in any danger from this event. Even though it sounds terrifying — an explosion the equivalent of billions of nuclear weapons launching hundreds of millions of tons of subatomic particles Earthward at speeds of million of kilometers per hour! — we’re pretty well protected down here on the surface. The Earth’s magnetic field catches the particles, and most of those get dumped harmlessly in our upper atmosphere. That can create the aurora displays, but won’t dose everyone with radiation and give them superpowers.
Sorry. [UPDATE (19:00 UTC): a ground current surge was reported in Sweden, but so far that's the only physical impact I've heard of.]
But the aurorae are pretty cool, and that brings us to the second question. The answer depends on where you are, and when it’s dark out. As I write this, activity is on the rise. Here are some live webcams for aurorae, some of which are showing spectacular activity! Note they only show views when it’s nighttime locally:
I’m getting conflicting info on potential aurorae tonight; the webcams in Scandinavia listed above are showing strong (and gorgeous) activity, but the prediction for Canada and the US appear moderate at best. But don’t let that discourage you! If you have clear skies, go outside once it’s good and dark and take a look. Even if there’s no aurora, you can see Venus and the thin crescent Moon to the west right after sunset, and that’s always a plus. And if things perk up, you might get a nice light show to the north, too!
Around 04:00 UTC on Monday morning, January 23, 2012, the Sun let loose a pretty big flare and coronal mass ejection. Although there have been bigger events in recent months, this one happened to line up in such a way that the blast of subatomic particles unleashed headed straight for Earth. It’s causing what may be the biggest space weather event in the past several years for Earth: people at high latitudes can expect lots of bright and beautiful aurorae.
I’ll explain what all that is in a second, but first here’s a video of what this looked like from NASA’s SOHO satellite.
Wow! Make sure you set it to high def.
So what happened here? The sunspot cluster called Active Region 11402 happened.
Sunspots are regions where the magnetic field lines of the Sun get tangled up. A vast amount of energy is stored in these lines, and if they get squeezed too much, they can release that energy all at once. When this happens, we call it a solar flare, and it can be mind-numbing: yesterday’s flare exploded with the energy of hundreds of millions of nuclear bombs!
In the image above, the sunspots are caught in mid-flare, seen in the far ultraviolet by NASA’s Solar Dynamics Observatory (it’s colored green to make it easier to see what’s what). We think of sunspots as being dark (see the image of AR 11402 below), but that’s only in visible light, the kind we see. In more energetic ultraviolet light, they are brilliant bright due to their magnetic activity.
A huge blast of subatomic particles was accelerated by the explosion. The first wave arrived within a few of hours of the light itself… meaning they were traveling at a significant fraction of the speed of light!
But shortly after the flare there was a coronal mass ejection: a larger scale but somewhat less intense event. This also launches particles into space, and these are aimed right at us. The bulk of the particles are traveling at slower speeds — a mere 2200 km/sec, or 5 million miles per hour — and is expected to hit us at 14:00 UTC Tuesday morning or so. That’s basically now as I write this! Those particles interact with Earth’s magnetic field in a complicated process that sends them sleeting down into our atmosphere. We’re in no real danger from this, but the particles can strip the electrons off of atoms high in the air, and when the electrons recombine the atoms glow excite the electrons in atoms high in the air, and when the electrons give up that energy the atoms glow. That’s what causes the aurorae — the northern and southern lights.
If you live in high latitudes you might be able to see quite the display when it’s dark — people in eastern Europe and Asia are favored for this, since this happens after sunset there. But the storm is big enough and will probably last long enough that everyone should check after dark: look north if you live in the northern hemisphere and south if you’re south of the Equator. There’s no way in advance to know just how big this will be; it might fizzle, or it might be possible to see it farther away from the poles than usual. Can’t hurt to look! Also, Universe Today has been collecting pictures of aurorae from the solar blast earlier this week. No doubt they’ll have more from this one as well.
As I said, we’re in no real danger here on Earth, and Universe Today has a good article describing why the astronauts are probably not in danger on the space station, either. Even if this were larger storm, the astronauts can take shelter in more well-protected parts of the station, too. Bigger storms can hurt us even on Earth by inducing huge currents in power lines which can overload the grid. That does happen — it happened in Quebec in March of 1989 — and it may very well happen again as the Sun gets more active over the next few years. [UPDATE: a ground current surge from today's event was reported in Norway.]
But we should be OK from this one. If you can, get outside and look for the aurorae! I’ve never seen a good one, and I’m still hoping this solar cycle will let me see my first.
As the Sun rotates roughly once per month, we see different features come into view… and the latest is an enormous sunspot system which just came around the limb of the Sun:
[Click to magneticfieldentanglenate.]
That shot was taken by the Mexican "amateur" astronomer César Cantú, and shows the spots — called Active Region 1339 — from November 4. The size of this system is staggering; the whole thing is well over 100,000 km (60,000 miles) across, and the dark cores are each about the size of our entire Earth!
They’re active, too: On November 3rd they popped off a pretty big X 1.9 class flare:
That image was taken by NASA’s Solar Dynamics Observatory in the ultraviolet, where violent activity is easier to see. NASA made a video of the flare, and you should take a look. It’s pretty amazing.
So we have a recipe for some action here: big spots, known to be active, and they’re riding the Sun’s surface as it rotates them more fully toward us. Over the next week and a half we might get some more flares from them, and maybe some coronal mass ejections… and that means we might get more aurorae. Stay tuned here; if any occur I’ll report them as soon as I hear. Also keep your browser pointed at SpaceWeather.com, which always has the latest info as well.
But the flares don’t have to be so powerful to generate ethereal, magnificent beauty. A day after that biggish event, those sunspots burped again, this time with a lower-power M-class flare. Now, when I say "low power", it’s not like a firecracker or a car backfiring: the total energy released would still dwarf the combined nuclear might of every country on Earth! By a lot. But for the Sun, that’s considered to be "meh".
[Make sure to set it to at least 720p and make it full screen!]
The flare and prominence — the arcing tower of material — lasted about three hours, and this video shows it at a rate of one frame every minute of real time. The flare pops, and then the fountain erupts from the surface. This gas is ionized (stripped of at least one electron), so it’s highly influenced by the magnetic field of the Sun as well as by its crushing gravity. The material flows up, forming that amazing sheet of roiling gas, reaches the top of its arc, and falls back down.
Well, it doesn’t fall so much as flow, guided by the enormous strength of the Sun’s magnetic field lines. Mind you, eyeballing from the size of the Sun’s disk, I’d venture this tower of gas is well over 100,000 km (60,000 miles) long! There are millions of tons of gas in it as well, moving dozens of times faster than a rifle bullet. The energies involved are mind-crushing.
Also, if you look to the upper left, you’ll see a smaller prominence loop caught in the act of evolving, with material apparently floating over the solar surface, then flowing back down as well.
But shortly after the flare there was a 
Well, it doesn’t fall so much as flow, 
