A large-scale structure seen in white-light images of the Sun's corona. Streamers are brighter than the surrounding corona because they are of higher density, and are often bottle-shaped, narrowing away from the Sun. They are also referred to as helmet streamers because of their resemblance to a helmet with a spike on top. The broad base of the streamer is where coronal plasma is trapped along closed magnetic field lines, but at larger distances the magnetic field weakens and the plasma is able to break free from the Sun, producing the narrow spike. Streamers are principally found above active regions and prominences, but also occur at solar minimum when there are few or no active regions. In the latter case, two streamers are seen on opposite sides of the Sun, close to the equator. They are a projection of a streamer belt that encircles the Sun. At the poles of the Sun during solar minimum the magnetic field opens out directly into space, and narrow coronal plumes are found to lie along these field lines.
Subjects: Astronomy and Astrophysics.