The Sun, a massive sphere of superheated plasma, cannot be viewed “up close” in the traditional sense. Advanced spacecraft like the Parker Solar Probe and Solar Orbiter have provided unprecedented views of its complex layers. These missions reveal a dynamic, layered body where powerful magnetic forces drive constant, explosive change. Understanding what the Sun looks like up close requires examining its visible surface and the energetic processes that extend far into space.
The Sun’s Visible Surface
The layer we perceive as the Sun’s surface is the photosphere, the point where light finally escapes. Up close, the photosphere appears not smooth, but covered in a texture resembling boiling rice, a phenomenon called granulation. These granules are the tops of convection cells, each typically measuring around 1,100 kilometers across, roughly the size of a small country.
The brighter centers of these cells mark where hot plasma rises from the Sun’s interior, while the darker, cooler edges are where the plasma sinks back down. This constant churning shows the energy transfer that powers the star. The plasma flows within these cells can reach speeds of several kilometers per second.
Sunspots appear as darker regions because they are significantly cooler than the surrounding photosphere (about 5,700 Kelvin). The inner, darkest part of a sunspot, called the umbra, can drop to around 3,700 Kelvin. Sunspots form where concentrated magnetic field lines suppress the normal convective flow of heat from the solar interior. A less dark region called the penumbra surrounds the umbra, marking where the magnetic field is weaker. These magnetic structures can persist for days or weeks, often growing to sizes comparable to the diameter of Earth.
Magnetic Activity and Solar Eruptions
The magnetic field that creates sunspots powers the Sun’s most dramatic, transient phenomena. One such event is the solar flare, a sudden, powerful burst of electromagnetic radiation released when magnetic field lines in the corona rapidly reconnect. These flares release energy equivalent to millions of hydrogen bombs in a matter of minutes, causing a dramatic brightening in X-ray and ultraviolet light.
Often originating near complex sunspot groups, flares are categorized by their intensity, from the weakest A-class to the most powerful X-class. The energy from these events heats the localized plasma to several million degrees Kelvin, accelerating charged particles to near the speed of light. Solar flares are distinct from the physical expulsion of matter, though they frequently occur together.
Prominences are massive, looping structures of relatively cool, dense plasma suspended above the photosphere by strong magnetic fields. When viewed at the Sun’s edge, these structures appear bright and arching, sometimes extending over 100,000 kilometers into space. When viewed against the bright solar disk, the same structure appears as a dark, elongated ribbon called a filament, because its cooler plasma absorbs the light from the hotter surface below it.
The most powerful eruptions are Coronal Mass Ejections (CMEs), which are huge expulsions of plasma and magnetic field. A CME can eject billions of tons of material into space at speeds ranging from 250 kilometers per second up to 3,000 kilometers per second. These massive clouds of magnetized material expand as they travel, often originating from the eruption of an unstable prominence.
The Extended Outer Atmosphere
Immediately above the photosphere is the chromosphere, a thin layer of gas visible only during a total solar eclipse. This layer gets its name, meaning “color sphere,” from its reddish glow, caused by the emission of light from hydrogen atoms. The chromosphere is marked by spicules, which are dynamic, short-lived jets of plasma that shoot upward from the layer at high speeds, reaching heights of thousands of kilometers.
Beyond the chromosphere lies the corona, the Sun’s vast, tenuous outer atmosphere that stretches millions of kilometers into space. The corona is a striking feature when seen during an eclipse, appearing as a pearly white crown of light surrounding the dark silhouette of the Moon. It is characterized by complex magnetic structures, including magnetic loops that channel the superheated plasma.
The corona presents one of the biggest mysteries in solar physics because it is paradoxically much hotter than the surface below it. While the underlying photosphere has a temperature of about 5,700 Kelvin, the corona can spike to over one million Kelvin. Scientists are exploring theories that involve energy being transported upward by various types of waves or dissipated through millions of tiny, localized magnetic explosive events.
The outermost edge of the corona is the source of the solar wind, a constant stream of charged particles and magnetic fields that flows outward into the solar system. This supersonic wind carries the Sun’s influence far beyond the orbits of the planets, filling the entire heliosphere. The outflow of this plasma completes the picture of a star continuously reshaped by its powerful magnetic forces.