Solar corona

The Sun’s outer atmosphere extends millions of kilometers into space and reaches temperatures far higher than its visible surface.

Coronal heating problem: The unresolved question of how the Sun’s corona reaches temperatures far above its visible surface. It captures the central puzzle of the corona’s extraordinary temperature.
Coronal mass ejection: A large eruption of magnetized plasma from the Sun’s outer atmosphere. These eruptions carry coronal material and magnetic fields into space.
Total solar eclipse: An eclipse in which the Moon completely covers the Sun’s bright photosphere as seen from a location on Earth. Totality makes the faint corona visible against the darkened sky.
Solar photosphere: The Sun’s visible surface layer, from which most of its visible light escapes. The photosphere is far cooler and brighter than the corona.
Magnetic reconnection: A process in which magnetic-field lines rearrange and release stored energy in a plasma. It can rapidly deposit magnetic energy into coronal plasma.
Space weather: The changing conditions in space driven chiefly by solar activity and its effects on Earth and other bodies. Coronal activity is a major source of disruptive space-weather events.
Parker Solar Probe: A NASA spacecraft launched in 2018 to study the Sun’s corona and solar wind from close range. Its repeated close passes sample the corona and its escaping plasma.
Solar chromosphere: A thin atmospheric layer above the photosphere and below the solar transition region. The chromosphere lies beneath the corona and has different temperatures and spectral features.
Alfvén wave: A transverse wave that travels through a magnetized plasma by coupling magnetic fields to fluid motion. Alfvén waves can carry energy from the solar surface into the corona.
Geomagnetic storm: A disturbance of Earth’s magnetosphere caused by enhanced solar-wind energy transfer. A geoeffective coronal mass ejection can trigger a geomagnetic storm.

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