37 articles
Alfvén surface
The Alfvén surface is the boundary around a magnetized star where the solar wind outruns the Alfvén speed, first crossed by Parker Solar Probe in 2021.
Butterfly diagram
The butterfly diagram is a time–latitude plot of sunspots, first drawn by Edward Maunder in 1904, showing spots migrate from mid-latitudes toward the equator over each solar cycle.
Chromosphere
The chromosphere is the roughly 2,500 km thick layer of the Sun's atmosphere above the photosphere, glowing red from hydrogen-alpha emission and visible during total eclipses.
Convection zone
The convection zone is the Sun's outermost interior layer, where convection rather than radiation carries energy to the visible surface, spanning the outer third by radius.
Coronal heating problem
The coronal heating problem is the unsolved question of why the Sun's outer atmosphere, the corona, reaches 1–2 million kelvin while the surface below is only about 6000 K.
Coronal hole
A coronal hole is a dark, cooler, less dense region of the Sun's corona with open magnetic field lines, the source of the fast solar wind.
Coronal loop
A coronal loop is an arch-shaped structure of hot plasma in the Sun's corona following closed magnetic field lines, best seen in X-ray and ultraviolet telescopes.
Coronal mass ejection
A coronal mass ejection (CME), also called a coronal transient, is a large eruption of magnetized plasma from the Sun's corona that drives the strongest geomagnetic storms at Earth.
Coronal rain
Coronal rain is cool, dense plasma condensing in the Sun's corona that falls along magnetic loops, formed by thermal instability and used to probe coronal heating.
Differential rotation
Differential rotation is when different latitudes of a gaseous body rotate at different speeds, seen in the Sun, where the equator spins in 25 days and the poles in 36.
Filament eruption
A filament eruption is the sudden ejection of a solar filament, cool dense plasma held above the Sun by magnetic fields, into space or the solar atmosphere.
Gleissberg cycle
The Gleissberg cycle is an 80- to 100-year modulation of the Sun's 11-year sunspot cycle, named for German astronomer Wolfgang Gleissberg, who described it around 1938.
Hale cycle
The Hale cycle is the Sun's approximately 22-year magnetic cycle, named for George Ellery Hale, who discovered sunspot magnetic fields in 1908; its polarity reverses at each 11-year sunspot cycle.
Heliotail
The heliotail is the trailing region of the heliosphere, extending opposite the Sun's motion through the galaxy like a wake, first imaged by NASA's IBEX mission in 2013.
Photosphere
The photosphere is the visible surface of the Sun, the lowest layer of the solar atmosphere, which emits most of the Sun's light at about 5,500 °C.
Radiative zone
The radiative zone is the layer of the Sun's interior between the core and the convection zone, where energy travels outward as photons over more than 170,000 years.
Solar Activity
Solar activity: magnetic phenomena on the Sun, including sunspots, solar flares, coronal mass ejections, solar wind, and solar energetic particles, varying over an 11-year solar cycle and driving space weather that affects satellites, GPS, radio, and power grids on Earth.
Solar campfires
Solar campfires are small, transient extreme-ultraviolet brightenings in the quiet solar corona, first seen in 2020 by Solar Orbiter and studied as possible contributors to heating the Sun's million-degree corona.
Solar composition
Solar composition is the measured abundance of chemical elements in the Sun, determined from photospheric spectroscopy, CI chondrite meteorites, and Genesis solar wind samples; it serves as the reference for stellar chemistry.
Solar core
The solar core is the Sun's central region, where nuclear fusion of hydrogen into helium produces about 98% of the Sun's energy at roughly 15,000,000 °C.
Solar corona
The solar corona, also called the Sun's corona, is the outermost layer of the Sun's atmosphere, hotter than the surface below it at over 1 million degrees Celsius.
Solar cycle
The solar cycle, also known as the Schwabe or sunspot cycle, is the roughly 11-year rise and fall of the Sun's magnetic activity, tracked by sunspot numbers.
Solar cycle prediction
Solar cycle prediction is the forecasting of the amplitude and timing of an upcoming or ongoing solar cycle, the Sun's roughly 11-year oscillation in magnetic activity.
Solar dynamo
The solar dynamo is the hydromagnetic process inside the Sun that generates its large-scale magnetic field, driving the 11-year sunspot cycle and the 22-year polarity reversal cycle.
Solar flare
A solar flare, also called a Sun flare, is an intense burst of radiation from magnetic energy at sunspots, the solar system's most powerful explosion.
Solar granulation
Solar granulation is the mottled pattern of bright convection cells on the Sun's surface, where granules 700 to 1000 km wide live 5 to 10 minutes.
Solar irradiance variability
Solar irradiance variability is the variation over time of the Sun's radiant power at Earth, averaging about 1361 W/m² and fluctuating roughly 0.1% over the 11-year solar cycle.
Solar luminosity
Solar luminosity is the total rate at which the Sun emits energy, about 3.828×10²⁶ watts; astronomers use it as a standard unit for expressing other stars' power output.
Solar magnetic field
The solar magnetic field is the magnetic field generated inside the Sun by a dynamo, producing sunspots and flares, with polarity reversing roughly every 11 years.
Solar prominence
A solar prominence is a large, bright structure of cool, dense plasma extending from the Sun's surface into the hot corona, held by magnetic fields; many erupt, driving space weather.