Sunspot
Definition
A dark, cooler patch on the Sun marking intense magnetic activity — the source regions of flares and CMEs.
In plain language
Sunspots look dark because they are a few thousand degrees cooler than their surroundings, held that way by powerful magnetic fields. Those tangled fields are loaded springs: when they snap, flares and CMEs fly.
The science
Sunspots are photospheric regions of kilogauss-strength magnetic flux that suppresses convection. Complex spot groups (delta configurations) are statistically most productive of M/X flares and fast CMEs. Counts follow the 11-year cycle.
Why it matters for aurora viewing
More and messier sunspots facing Earth means higher odds an aurora-driving eruption is coming your way this week.
See this in action on tonight's data.