Coronal Holes and Active Regions
This image at left from Yohkoh shows the Solar corona. The bright features represents magnetically-trapped plasma. In contrast, the dark regions, known as coronal holes, are where the Sun's magnetic field extends out into space, allowing the hot gas to escape. These regions contain material which is cooler than the surrounding ~106 K plasma seen in soft X-rays, and often appear near the Sun's poles as seen above.
Active regions are formed when magnetic field lines of the Sun emerge from the photosphere and open into the corona. Hot gas is visible near the magnetic field, making bright loops. Active regions may last for several weeks or even several months. Sunspots (image at right) are often associated with active regions, as seen above.