Right now as I write this, the Sun is settling down after a minor flare tripped a flippin' huge and spectacular prominence: a looping tower of plasma hundreds of thousands of kilometers high! Using Helioviewer.org, I created a short movie of the eruption, and you just have to see it. Make sure you have the resolution set to hi-def!
Isn't that amazing? The flare that triggered this event was no big deal, about an M1.7, which is nothing to worry about at all. We had far bigger ones in March! But that arc of plasma -- ionized gas -- is astonishing. Flares happen when the magnetic field lines of the Sun get tangled, and suddenly release their vast, vast stored energy. The erupting plasma follows those field lines up and away from the Sun. Some escapes forever, and some falls back to the surface. You can easily see it flowing in these videos.
These views show the eruption in two different wavelengths, though both are in the ultraviolet, where the magnetic activity is easiest to see. My friends at NASA Goddard put up some fantastic pictures of it, like the one above [click to embiggen]. They have some video there, too.
I'll note that the active region shown here is on the side of the Sun rotating toward the Earth right now, so if there are more eruptions in the next few days we may see some affect on Earth, like aurorae at northern latitudes. As usual, you don't need to panic about this stuff. The worst it can realistically do here on Earth is cause blackouts if a particularly big storm overloads our power grid. And while that would be irritating, it's unlikely. So sit back and enjoy the show!
[Edited to add: Some folks are asking how long this event took; it went from start to finish in just a few hours. Another common question is how big the Earth would be compared to this, and the answer is: really really teeny. Check out the curve of the Sun's edge, and remember that the Sun is over 100 times the diameter of the Earth!] Credits: NASA/SDO/helioviewer.org. Music: "Feral Chase" by Kevin MacLeod.
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