A faint feature in the Sun's corona that extends radially out from coronal holes at the Sun's poles; also referred to as a polar plume. Coronal plumes can be seen at the Sun's limb in visible light with coronagraphs and during eclipses, as well as in ultraviolet emission lines formed at temperatures around 1 million degrees. The bases of the plumes can be identified on the Sun's disk at ultraviolet wavelengths as areas of bright emission in coronal holes. Plumes have been traced out to at least fifteen solar radii on images from the SOHO spacecraft. Plumes are usually denser and cooler than their surroundings, and are most easily identified during solar minimum when coronal holes are clearly seen at the poles of the Sun. There is as yet no conclusive evidence for plumes in equatorial coronal holes.
Subjects: Astronomy and Astrophysics.