Thread by @ScottWx_TWN

There's a single sunspot visible on the Earth-facing side the Sun right now.
Three Earths could fit, side-by-side, across it! Lots of activity around it, too. Look at those coronal loops! #spaceweather #TheSun

If you're curious what's going on here, the Sun is basically a giant ball of charged particles (plasma), boiling from the heat of the fusion reactions at its core. As all those charged particles circulate around inside the Sun, and at its surface, they produce magnetic fields.

The magnetic fields add up to produce the huge bubble that surrounds the solar system (called the Heliosphere), but there are also many (many, many) smaller magnetic fields, and some of these poke out of the surface. We see these as the coronal loops.

If you remember what the ideal look of a magnetic field is like, either with a bar magnet or Earth's magnetic field, there are looping field lines. Coronal loops are similar, but way more chaotic, because it's many different magnetic fields, all pressed up against each other.

They glow like that, because the plasma particles - which are at temperatures of around 1 million degrees Kelvin - are drawn up along the field lines. The glow is brighter where they're more concentrated, and dimmer where they're more diffuse.

The sunspot forms due to the magnetic field lines protruding from the surface. Normally, material at the surface is quickly circulated back down under & is replaced by hot material from below.
When the field lines get tangled up, though, it prevents that material from sinking.

So, that material trapped at the surface keeps radiating heat away into space, and it cools down... and when we take pictures like this one, which focus on a very specific range of temperatures, the sunspot looks darker than the surrounding, hotter, material.

Since this is just a situation of chaos, there are several things that can happen here.
The sunspot can just remain pretty stable all the way across the face of the Sun.
It can become more complex, as more & more magnetic fields get tangled up, producing a cluster of dark spots.

The field lines can become so tangled up that they cause a sudden, violent "reconnection", as that tangle unravels. This is a "solar flare". It's like tying a rubber band into knots & then it snapping... except in this case, the "snapping" releases an incredible burst of energy.

Here's a pair of solar flares, caught by NASA in June 2014.
The first was an X2.2 flare. The second, although brighter, was an X1.5 flare.

The second one appears longer and brighter, but I believe it was classified as weaker than the first, because the first one was more sudden, releasing more energy in a shorter time span. In both cases, though, you can see that some solar material is blasted off to the left.

These clouds of solar matter, blasted away from the solar flare, are known as 'coronal mass ejections'.
The're basically eruptions of solar plasma, which then expand out into space.
(This animation is from a different solar flare, from 2017, but it's a good example)

As huge clouds of moving charged particles, CMEs carry magnetic fields along with them, and when they reach Earth, that collective magnetic field interacts with Earth's geomagnetic field. This can produce auroras!

I need to take off for lunch, but I'm going to leave you with this, for now... Coronal Loops are probably my favourite space weather/solar activity phenomenon. These are just beautiful.
(video from @NASAGoddard)