The Solar Atmosphere

The reddish layer of the solar atmosphere just above the photosphere, a few thousand kilometres thick, briefly visible as a rosy rim at the start and end of a total eclipse. Its temperature rises with height, and it is threaded by spicules, filaments, and plages. Above it lies the thin transition region.

The visible surface of the Sun — the layer from which sunlight escapes — with an effective temperature near 5,772 kelvin and a thickness of only a few hundred kilometres. Sunspots, granulation, and the limb darkening seen in white-light images all belong to the photosphere. It is the reference surface for the Sun's radius.

The Sun's outermost atmosphere — a tenuous, million-degree plasma extending millions of kilometres into space, visible to the eye only during a total solar eclipse or with a coronagraph. Far hotter than the surface beneath it, it is shaped by magnetic fields into loops, holes, and streamers, and it continually expands outward as the solar wind.

The thin, irregular layer between the chromosphere and the corona where the temperature climbs steeply — from around ten thousand to a million kelvin over only a few hundred kilometres. It radiates mostly in the extreme ultraviolet and is central to the still-open question of how the corona is heated.

An arch of hot, glowing plasma tracing a magnetic field line rooted in the photosphere, the basic building block of the closed corona above active regions. Coronal loops shine brightly in the extreme ultraviolet and X-rays and are central to studies of how the corona is structured and heated.

A large, pointed structure in the corona, seen in eclipse and coronagraph images as bright rays extending outward above the streamer belt. Helmet streamers cap closed magnetic regions and are the source of the slow solar wind; their shape changes over the solar cycle.

The same structure as a prominence, but seen against the bright solar disk rather than at the limb, where it appears as a dark, thread-like channel. A filament is cool plasma along a magnetic boundary; its sudden eruption is a common trigger of a coronal mass ejection.

The mottled, cellular pattern covering the photosphere — the tops of convection cells about a thousand kilometres across, each lasting only minutes. Bright centres are hot plasma rising, dark lanes are cooler plasma sinking. Granulation is the direct visible signature of the convection zone beneath.

A bright region of the chromosphere associated with an active region, where concentrated magnetic field heats the plasma above a group of sunspots. Plages are conspicuous in the light of hydrogen and calcium and mark magnetically active areas even as the sunspots themselves come and go.

A thin, ray-like structure of denser plasma rooted in the Sun's polar regions and extending into a polar coronal hole. Plumes trace open magnetic field lines from which fast solar wind flows, and appear as delicate streaks in images of the poles.

A large, relatively cool and dense structure of plasma suspended above the solar surface by magnetic fields, extending into the hot corona. Seen at the limb against the dark sky it appears as a bright arch; quiescent prominences can last for months, while eruptive ones can launch a coronal mass ejection.

A short-lived jet of plasma, a few hundred kilometres across, that shoots up from the chromosphere at tens of kilometres per second and falls back within minutes. Millions cover the Sun at any moment, giving the chromospheric limb a grassy appearance; they may contribute to the mass and energy budget of the corona.

A larger-scale convective pattern, with cells around thirty thousand kilometres across that persist for roughly a day. Supergranule flows sweep magnetic field to their edges, building the chromospheric network. It was discovered through Doppler measurements of the surface flows.