A solar prominence is a large, bright feature extending outward from the Sun’s surface, often in a loop shape, consisting of relatively cool, dense plasma suspended above the Sun’s photosphere by magnetic forces. These structures are anchored in the Sun’s photosphere and extend outward into the corona, the Sun’s outer atmosphere. Prominences consist of of hydrogen and helium plasma, and despite their lower temperature compared to the corona, they remain suspended due to strong magnetic fields.
Solar prominences can last from days to weeks, and their sizes are immense — often tens to hundreds of thousands of kilometers long, with heights reaching over 100,000 km. Some are longer than the diameter of Earth. When these prominences become unstable and erupt, they sometimes produce coronal mass ejections (CMEs), hurling solar material into space.
Key Points About Solar Prominences
- Solar prominences are large, bright plasma structures extending from the Sun’s surface into its corona.
- They are cooler, denser hydrogen and helium compared to their surroundings.
- Magnetic fields support and shape prominences, forming loops or sheets.
- Prominences can persist for days or weeks; eruptions may lead to CMEs.
- Some prominences span over 100,000 km — much larger than Earth.
- They are visible during solar eclipses or with special solar observation filters.
- Prominences are categorized as quiescent, active, or eruptive.
- Though dramatic, they pose little direct danger to humans on Earth.
History of Discovery and Study
Solar prominences were first documented in the 14th century in the Laurentian Codex, but their true nature remained unclear until the advent of telescopic solar observation. In 1643, French monk Jean Tarde described them during a total solar eclipse. The term “prominence” was first used by astronomers like Pierre Jules Janssen and Joseph Norman Lockyer in 1868, who independently observed prominences and discovered the spectral line of helium.
By the 20th century, the development of spectroheliographs, H-alpha filters, and space-based telescopes allowed continuous observation and deeper understanding of their structure, formation, and role in solar activity.
Appearance and Features (Morphology)
Solar prominences are visually striking plasma structures shaped and supported by the Sun’s magnetic field. They typically appear as loops, curtains, or elongated threads of bright, glowing plasma when viewed above the solar limb and as dark solar filaments when viewed against the bright solar disk in the H-alpha spectral line..
Their morphology includes several key components and surrounding structures:
Spine
The spine is the main, elevated body of the prominence — a horizontal, thread-like structure of relatively cool, dense plasma suspended in the Sun’s hot corona. It runs along the magnetic neutral line where opposite polarities meet and is supported by horizontal magnetic fields.
Pillars (or Footpoints/Legs)
Pillars are the vertical or slightly inclined structures that anchor the prominence to the photosphere. They trace out magnetic field lines rising from sunspots or plages and help channel plasma into and out of the prominence.
Barbs
Barbs are short lateral extensions from the spine, resembling branches. Barbs are believed to mark where magnetic field lines dip down to the chromosphere, allowing plasma to drain or accumulate. They likely play a role in anchoring the prominence.
Filament Channel
A filament channel is the underlying magnetic structure in the chromosphere where a filament or prominence forms. It lies above the polarity inversion line (PIL) — a boundary separating regions of opposite magnetic polarity — and shows aligned chromospheric fibrils and horizontal fields. The filament spine typically forms above this channel.
Magnetic Arcade
Overlying many prominences is a magnetic arcade: a set of coronal loops formed by closed magnetic field lines. These arcades trap hot coronal plasma and play a stabilizing role. When the arcade is disrupted, it can trigger prominence eruptions.
Cavity
Some prominences lie within a coronal cavity, a dark, elliptical or teardrop-shaped void in coronal images. The cavity surrounds the magnetic flux rope and appears darker due to reduced plasma density. It is often seen in EUV or soft X-ray wavelengths.
Helmet Streamer
Above many quiescent prominences lies a helmet streamer, a large-scale coronal structure resembling a pointed helmet. Helmet streamers are shaped by the outward extension of closed magnetic field lines and are closely tied to the global magnetic field configuration. They form the bright, smooth streamers seen in white-light coronagraph images during solar eclipses and can extend millions of kilometers into the solar wind.
Solar Prominence Chirality (Magnetic Handedness)
Chirality refers to the magnetic handedness or asymmetry of a filament or prominence structure, describing the direction in which magnetic field lines twist relative to the solar surface:
- Dextral chirality: Field lines point to the right when viewed from the positive polarity side (predominant in the northern hemisphere).
- Sinistral chirality: Field lines point to the left (more common in the southern hemisphere).
Chirality helps determine the configuration of barbs and the direction of axial magnetic fields. It plays a significant role in prominence stability, helicity, and eruption dynamics, and it may reflect the large-scale hemispheric patterns in solar magnetism.
Classification of Solar Prominences
Prominences are classified based on their behavior, location, and magnetic environment:
By Behavior:
- Quiescent Prominences
- Large, stable, and long-lived (days to weeks).
- Found in quiet regions of the Sun.
- May become eruptive.
- Active Prominences
- Smaller and shorter-lived.
- Rapid changes and motion, often associated with sunspot regions.
- Eruptive Prominences
- Unstable prominences that rise and expel plasma into space.
- Often associated with CMEs and solar flares.
By Shape:
- Loop Prominence: Arches or loops anchored at both ends.
- Hedgerow Prominence: Rows of small column-like structures.
- Sheet or Curtain Prominence: Wide and flat in appearance.
Prominence Eruptions
A prominence eruption occurs when the magnetic structure supporting the prominence becomes unstable, causing the plasma to rise and be ejected into space. This can happen gradually or explosively and may coincide with:
- Solar flares: Bursts of radiation caused by magnetic reconnection.
- Coronal mass ejections (CMEs): Huge clouds of solar plasma and magnetic field ejected into the solar system.
Eruptions can affect space weather, disrupting satellites, radio communications, and even power grids on Earth during geomagnetic storms.
Theories of Solar Prominence Formation
Prominences form in regions where the Sun’s magnetic field lines trap cooler plasma above the surface. Two main theories describe this process:
- Magnetic Flux Rope Theory
- Prominences form along twisted magnetic fields (flux ropes) that rise through the solar atmosphere and trap plasma.
- Sheared Arcade Model
- Prominences are suspended along magnetic arcades that have been distorted or sheared by differential motion in the photosphere.
Both models rely on magnetic reconnection and the buildup of magnetic stress, explaining the sudden eruptions and restructuring of the magnetic field.
Comparison With Related Phenomena
| Phenomenon | Description | Key Difference |
|---|---|---|
| Solar Filament | A prominence seen against the Sun’s disk as a dark line | Same structure; different viewing angle |
| Solar Flare | Sudden flash of brightness due to magnetic reconnection | More energetic, brief, not always tied to prominences |
| Coronal Mass Ejection (CME) | A massive burst of solar wind and magnetic field | Can be caused by eruptive prominences |
| Spicule | Small, short-lived jet of solar plasma | Much smaller and unrelated to magnetic loops |
Are Solar Prominences Dangerous?
Solar prominences themselves are not dangerous to life on Earth. However, eruptive prominences that trigger CMEs can affect:
- Satellites: Causing damage or loss of service.
- Power grids: Inducing geomagnetically induced currents (GICs).
- Astronauts: Increased exposure to radiation.
- Aviation: Disrupting high-frequency communication near the poles.
The Earth’s magnetosphere offers protection, but space-based and polar activities may require precautions during strong solar storms.
FAQs
Q: Can I see a solar prominence with the naked eye?
A: No, but they are visible through telescopes with H-alpha filters or during total solar eclipses.
Q: What color are solar prominences?
A: They typically appear red due to hydrogen emission lines, but color varies depending on the filter used.
Q: How hot is a solar prominence?
A: Around 5,000 to 8,000 K, much cooler than the million-degree corona.
Q: Do solar prominences affect weather on Earth?
A: Not directly, but eruptive prominences linked to CMEs influence space weather.
Q: How big can a solar prominence get?
A: Some stretch over 200,000 kilometers, many times the diameter of Earth.
Interesting Solar Prominence Facts
- The largest recorded solar prominence occurred on June 4, 1946, spanning over 350,000 km.
- The Sun’s magnetic activity cycle (about 11 years) influences prominence frequency.
- NASA’s Solar Dynamics Observatory (SDO) continuously monitors prominences in multiple wavelengths.
- In 1868, the study of solar prominences led to the discovery of the element helium, first detected in the Sun before being found on Earth.
References
- Galsgaard, K.; Longbottom, A.W. (1999). “Formation of solar prominences by flux convergence”. Astrophysical Journal. 510 (1): 444–459. doi:10.1086/306559
- Gopalswamy, N.; Shimojo, M.; Lu, W.; Yashiro, S.; Shibasaki, K.; Howard, R. A. (2003). “Prominence Eruptions and Coronal Mass Ejection: A Statistical Study Using Microwave Observations”. The Astrophysical Journal. 586 (1): 562–578. doi:10.1086/367614
- Low, B.C.; Fong, B.; Fan, Y. (2003). “The mass of a solar quiescent prominence”. Astrophysical Journal. 594 (2): 1060. doi:10.1086/377042
- Mackay, D. H.; Karpen, J. T.; Ballester, J. L.; Schmieder, B.; Aulanier, G. (2010). “Physics of Solar Prominences: II – Magnetic Structure and Dynamics”. Space Science Reviews. 151 (4): 333–399. doi:10.1007/s11214-010-9628-0
- Vial, Jean-Claude; Engvold, Oddbjørn (2015). Solar Prominences. Springer. ISBN 978-3-319-10415-7.