The sun is constantly spewing high energy particles and radiation into space. This activity gets stronger and weaker in a cycle that takes about 11 years. We are currently in a low, but should be headed out of it anytime now. If fact, the low period is a bit longer than normal.
Even in the low periods, the sun can still burp, through a "solar flare" or a "coronal mass ejection". These particles interact with the upper atmosphere (like way high ~100+ km) and make the magical displays we all aurora.
