What is Solar Activity?
Solar activity refers to the time-varying phenomena on the Sun driven by its magnetic field: sunspots, solar flares, coronal mass ejections (CMEs), and the solar wind. These phenomena follow an approximately 11-year cycle (solar cycle). At solar maximum, activity is high—more sunspots, more flares, more CMEs. At solar minimum, activity is low. Solar activity is the driver of space weather at Earth: it causes geomagnetic storms, aurora, and effects on technology.
Sunspots
Sunspots are darker, cooler regions on the photosphere where strong magnetic fields emerge. They appear in pairs or groups and are the main visible tracer of the solar cycle. More sunspots mean more flares and CMEs.
Flares and CMEs
Solar flares are sudden bursts of radiation (X-rays, UV) from the Sun's atmosphere; they reach Earth in ~8 minutes. CMEs are eruptions of plasma and magnetic field; they take 1–3 days to reach Earth and can trigger geomagnetic storms. Cosmic Radar shows reported flares and CMEs in the daily report together with the Kp index and aurora outlook.
Sources and further reading
- NOAA Space Weather – Solar activity, flares, CMEs, Kp
- NASA SDO – Solar images and activity
- ESA Space Weather – European monitoring