Active Regions on the Sun

Active Regions on the Sun

Solar Active Regions - Sunspots and UV Image

Two views of active regions: a closeup of sunspots (top) and coronal loops in an ultraviolet image of the Sun's atmosphere (bottom).
Credit: Royal Swedish Academy of Sciences - Göran Scharmer and Mats Löfdahl (sunspots) and NASA/SDO and the AIA, EVE, and HMI science teams (coronal loops).

An active region on the Sun is an area with an especially strong magnetic field. Most solar storms - solar flares and coronal mass ejections (CME) - blast forth from active regions.

Magnetic fields in active regions can be 1,000 or more times stronger than the average magnetic field of the Sun. Sunspots are visual indicators of active regions, although not all active regions produce sunspots. Sunspots are usually surrounded by lighter-shaded areas of mild magnetic disturbance called faculae (singular: facula). Some less intense active regions show up as just faculae without sunspots.

Active regions are most common during the peak of the sunspot cycle when the Sun's magnetic field is highly disturbed. Active regions appear bright in X-ray and ultraviolet images of the Sun. The powerful magnetic fields around active regions release intense bursts of energy, which often take the form of high-energy X-ray and UV photons. Many types of dramatic solar features, including solar prominences and coronal loops, frequently appear around active regions.

© 2014 UCAR