Understanding the Sun
A tour of the nearest star from the inside out — the fusion core, the radiative and convective interior, the visible surface and the million-degree corona, the magnetic activity and the eleven-year cycle, and the solar wind that blows the heliosphere out to the Voyagers.
Related entities
- Solar region
The Solar Corona
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.
- Solar region
The Solar Core
The innermost region of the Sun, out to about a quarter of its radius, where nuclear fusion powers the star. At roughly 15 million kelvin and immense density, hydrogen fuses to helium mainly through the proton–proton chain, releasing the energy that slowly works its way outward. Almost all of the Sun's luminosity is generated here.
- Stellar physics concept
The Solar Dynamo
The mechanism that generates and regenerates the Sun's magnetic field, converting the energy of plasma motions — differential rotation and convection — into magnetic energy. The dynamo drives the roughly eleven-year sunspot cycle and the reversal of the Sun's polarity; the details, especially the role of the tachocline, remain an active research problem.
- Heliosphere structure
The Parker Spiral
The spiral shape the Sun's magnetic field takes as it is carried outward by the solar wind while the Sun rotates, like water from a spinning sprinkler. Predicted by Eugene Parker in 1958 and since confirmed by spacecraft, the Parker spiral sets the geometry of the interplanetary magnetic field and how solar storms reach the planets.