The longest lightning bolts on Earth can extend for hundreds of kilometers, but even the longest produced by our planet’s clouds are dwarfed by the kind of discharges the Sun can produce. NASA's Solar Dynamics Observatory has caught a plasma discharge 500,000 kilometers long (which could wrap around the equator 12 and a half times) in the shape of a lightning bolt shooting through the Sun's atmosphere.
The Sun is approaching the peak of activity in its canonical 11 years cycle. There is an increase in the number of flares and coronal mass ejections, some even reaching our planet like the one that grazed us yesterday leading to increased activity in the Northern and Southern Lights.
Connected to this increase in activity is the increase in sunspots splotching the surface of the Sun. These regions are slightly cooler than the rest of the surface and are caused by magnetic fields rising from below the solar surface.
The magnetic field lines near sunspots can easily get messy as the Sun rotates. They tangle, cross, and reorganize, and these processes can release those flares and coronal mass ejections. Or in this case, just a harmless plasma discharge across the Sun, which still looks very cool.
Spaceweather.com reports that this “bolt” connected two sunspots, AR3192 and AR3190. The latter is pretty big. If you have eclipse glasses you should be able to see it with the naked eye without much trouble. A reminder though, for the love of your eyes, do not look at the Sun without proper glasses.