Active region

In solar physics, an active region is a temporary feature in the Sun's atmosphere characterized by a strong and complex magnetic field. Active regions are often associated with sunspots and are commonly the source of violent eruptions such as coronal mass ejections and solar flares. The number and location of active regions on the solar disk at any given time is dependent on the solar cycle.

The clearest definition of a solar active region is via its photospheric magnetic field; on a global magnetogram the active regions appear as complex bipolar structures. In the photosphere an active region consists of sunspots and faculae, and in the chromosphere, solar plages and an enhanced emission network that scales with the supergranulation. They typically persist for many solar rotations (months), following a relatively rapid initial growth. The strongest regions develop sunspots relatively early in their lifetime, but these normally decay and seldom persist for more than a single rotation.