Definition
Sunspots are darker, cooler regions on the Sun's photosphere (visible surface) where strong magnetic fields emerge from the interior. They appear darker because they are cooler (about 3,500 K vs. 5,800 K for the surrounding photosphere). They often appear in pairs or groups with opposite magnetic polarity.
Link to Flares and CMEs
Flares and CMEs often originate near sunspots, where magnetic field lines are concentrated and can reconnect. So sunspot number is a good proxy for solar activity. The 11-year solar cycle is defined by the rise and fall of sunspot count: solar maximum = many sunspots; solar minimum = few or none. Cosmic Radar shows space weather in the daily report; during high sunspot activity you'll see more flares and CMEs listed.
Sources and further reading
- NOAA – Sunspots and solar cycle – Official explanation
- NASA SDO – Sunspot and solar imagery
- ESA Space Weather – Solar monitoring