Hi Roger,

Solar flares are the biggest explosions in the solar system!

Flares are intense, rapid bursts of light (across wavelengths) observed on the disk of the Sun in active regions and have a large range in sizes. Flares are caused by magnetic fields becoming extremely stressed in an active region (think sunspot) and then rapidly releasing the energy that built up in the stressed field through various processes, ultimately resulting in reorganizing the field into a more relaxed state. This process causes particles in the thin atmosphere to be heated to millions of degrees and accelerated to near the speed of light. Some of those particles also crash into the denser surface. The heating and acceleration (positive and negative) all contribute to the sudden brightening of the flare.

Flares are often associated with eruptions of material as well, either as small jets or as enormous coronal mass ejections (CMEs). CMEs can be equivalent to the Sun ejecting a mountain's worth of plasma traveling at hundreds kilometers per second! You can see some great examples of CMEs at: https://sdo.gsfc.nasa.gov/gallery/main and https://sohowww.nascom.na.../Movies/flares.html.