Solar prominence

Prominences are concentrations of plasma—electrically charged gas—in the Sun’s outer atmosphere. They extend from the photosphere into the corona and are shaped and supported by magnetic fields. Although a prominence can look brilliant against the darkness of space, its plasma is cooler and denser than the surrounding coronal material. Its apparent brightness or darkness therefore depends in part on viewing geometry and contrast: seen projecting beyond the solar limb it is a prominence, while seen against the bright disk it is called a filament. The two terms describe different views of the same kind of solar structure.

Solar magnetic fields can form complex, curved structures that hold plasma above the visible solar surface. Prominences can develop over roughly a day and persist for days or, in stable cases, for months. Their detailed formation and the conditions that create or maintain them remain subjects of solar research. A structure can become unstable; in an eruption, plasma and magnetic fields move outward into the corona and may be released into interplanetary space.

Some prominence eruptions occur with coronal mass ejections (CMEs), large expulsions of plasma and magnetic field from the Sun. A CME can travel through interplanetary space and, if directed toward Earth, interact with the near-Earth environment. Prominence activity is consequently monitored as part of solar and space-weather research. However, a prominence eruption should not automatically be treated as a CME or as a prediction of an Earth impact: the details of each event, including its direction and properties, matter.

Solar observatories use several wavelengths to study prominences and their changing magnetic environment. Extreme-ultraviolet observations can reveal solar material and structures that are not visible to the unaided eye. At the solar limb, a prominence may appear as an arc or loop extending outward; on the disk, its filament counterpart can be seen as a darker feature. Comparing observations over time helps researchers follow changes in the structure and identify eruptions.