A solar flare occurs when sudden changes in the Sun’s magnetic field cause a cascade of particles (mostly electrons, I think) to accelerate violently and then, traveling along the magnetic field, smash into the surface* and ka-boom! Almost like a hyper-intense lightning strike. (Since the electrons are charged particles, it requires much less force for them to flow with the magnetic field than to cross it, so the currents follow the magnetic field lines.)

[*] Since the Sun is gaseous throughout, it doesn’t really have a surface, but the density rapidly becomes much greater (like thousands or millions of times) as you descend through the corona (which is close to a vacuum) end enter the photosphere (which is generally considered the “surface” of the Sun.) According to a graph I found , the photosphere is about 11 orders of magnitude denser than the corona, so the electrons act like they’ve hit a solid wall when the strike it.

A prominence is a big blob of gas (actually plasma) released into the corona by an active region on the Sun’s surface. They are cooler than the corona and appear as dark filaments when seen against the background of the Sun, but as bright prominences when they are near the limb of the solar disk and rise above it. Prominences often last for several days, versus solar flares which are all over in a few seconds. If a prominence is particularly energetic, instead of forming a big blobby loop through the corona, it will completely separate from the Sun and become a coronal mass ejection.

Prominences and flares (and sunspots, coronal loops, and lots of other solar phenomena) are all related to active regions, which are places where kinks in the Sun’s magnetic field poke up through the surface. As I understand it (I don’t think this view has been overturned in the last 30 years), during the 11 year solar cycle, differential rotation causes the magnetic field to twist up in the Sun. (The Sun rotates faster at the equator than at the poles.) Like the rubber band in a balsa wood airplane, eventually it forms kinks. Because of the twisting, the magnetic field of the kinks runs in the opposite direction of the field below the Sun’s surface. When the kinks poke through the surface, they form active regions and sunspots and produce loops, flare, prominences, and so forth.

As the differential rotation continues, more and more active regions get produced, until the total reversed field of the active regions exceeds the primary field and the whole magnetic system collapses, the Sun’s magnetic field reverses polarity, and another 11-year cycle starts, this time with a reversed field. So it is really 2 such cycles, or 22 years, to get back to the original condition.

One of my first jobs was to correlate Skylab EUV images with magnetic field observations from Kitt Peak and Sacramento Peak observatories, and compute the magnetic fields so they could be compared to the EUV images. I got mentioned in a foot note in Solar Physics, which is my scientific claim to glory.

The magnetic field lines matched up very nicely to the loops, which are generally anchored in sunspots of opposite magnetic polarities, like iron filings connecting the poles of a bar magnet.

From almost anywhere on land, the antipodal point is in an ocean. You would think by chance alone about 75% would be ocean, 25% land, since the earth is 75% ocean, but in fact almost none of the opposite points are on land. Just about the only exceptions are the southern tip of South America (Chile and Argentina) overlap with Asia, and parts of Australia overlap with Greenland, if I recall correctly. (I once got curious about this and checked.) This of course changes as the continents drift. In the time of Pangea, all the land was concentrated in one hemisphere. At other times, the continents were (or will be) more spread out and more likely to be opposite each other.

http://blogs.discovermagazine.com/badastronomy/2010/02/17/rocket-launch-blows-away-the-sky/

Methinks, *that*one should have been included there – perhaps the most spectacular shot of the SDO’s ever – even if it was inside its rocket at the time. How apt it blew away the Sun (“dog”) and is continuing to blow us away with it. May it do so for many years to come! 8)

Thanks SDO & thanks BA. I remember watching the launch of the SDO too. A year already?

What’s more, I think, the best is yet to come as the solar cycle ramps up.