A
Active Region — A magnetically complex area on the Sun’s surface where sunspots, flares, and CMEs are most likely to form.
Alfvén Speed — The speed at which magnetic disturbances travel through a plasma.
Alfvén Wave — A wave that moves along magnetic field lines as plasma and magnetic tension interact.
Alfvénic Fluctuations — Rapid, wave-like changes in the solar wind that behave like Alfvén waves.
Albedo — The fraction of light a surface reflects rather than absorbs.
Ap Index — A measure of daily global geomagnetic activity.
Aurora / Auroral Oval — Glowing atmospheric light caused by particles from space entering Earth’s poles.
Aurora Australis — The southern lights.
Aurora Borealis — The northern lights.
B
B-field (Magnetic Field) — The magnetic field strength and direction, often written as “B” in plasma physics.
Backside Event — A solar flare or eruption that happens on the far side of the Sun, out of Earth’s view.
Balmer Lines (H-alpha) — Specific hydrogen wavelengths used to study the chromosphere and filaments.
Bz (North–South IMF Component) — The part of the interplanetary magnetic field that controls how strongly the solar wind couples to Earth’s magnetosphere.
B-class Flare — A small solar flare with very low X-ray output.
Blackout (Radio Blackout) — A loss of radio communication caused by intense solar X-ray or EUV radiation.
C
C-class Flare — A modest solar flare that rarely causes major space-weather effects.
C2/C3 Coronagraph — SOHO’s instruments that block the Sun’s disk to reveal the corona and CMEs.
Carrington Coordinates — A longitude system that rotates with the Sun.
Carrington Rotation — A complete rotation of the Sun as seen from Earth, lasting about 27 days.
CME — Coronal Mass Ejection — A large eruption of plasma and magnetic field launched from the Sun into space.
CME Shock — A fast CME-driven disturbance that accelerates particles ahead of it.
Co-rotating Interaction Region (CIR) — A compressed part of the solar wind where fast wind catches slow wind.
Coronal Hole — A region of open magnetic field on the Sun that produces fast solar wind streams.
Coronal Loop — A bright, arching magnetic structure filled with hot plasma.
Coronal Rain — Cooler plasma that condenses and falls along magnetic loops in the corona.
Coronal Streamer — A large, bright structure in the corona formed by closed magnetic fields.
Corona — The Sun’s hot, extended outer atmosphere.
Cosmic Rays — Extremely energetic particles from the Sun, the galaxy, or beyond.
Cosmic Ray Modulation — Variations in cosmic-ray levels caused by changes in solar activity and the heliosphere.
Cross-field Diffusion — The process by which energetic particles wander across magnetic field lines.
Chromosphere — The thin solar layer above the photosphere where spicules and prominences originate.
Convection Zone — The outer part of the Sun where hot plasma rises and cooler plasma sinks.
Core (Solar) — The central region of the Sun where nuclear fusion occurs.
Cutoff Rigidity — The minimum energy a cosmic ray must have to reach the atmosphere at a given location.
D
D-region (Ionosphere) — The lowest part of the ionosphere that absorbs radio waves during solar flares.
Decametric Radio Burst — A solar radio emission seen at long wavelengths, often linked to flares or CMEs.
Delta Sunspot — A very magnetically complex sunspot with opposite polarities packed into one region.
Differential Rotation — The Sun’s equator rotates faster than its poles.
Diffusion Coefficient — A value describing how easily particles spread through magnetic turbulence.
Dipole Tilt — The angle between the Sun’s magnetic dipole axis and its rotational axis.
Dopplergram — An image that shows motion on the Sun using Doppler shifts.
E
EIT Wave — A large-scale EUV disturbance that ripples across the Sun during eruptions.
Electron Flux — The number of energetic electrons measured in space per unit time.
Electrojet — A strong electric current flowing around Earth’s auroral zones.
Ellerman Bomb — A small, short-lived brightening in the lower solar atmosphere.
EUV — Extreme Ultraviolet — A short wavelength of light used to image the solar atmosphere.
Event Fluence — The total number of particles or photons detected during an event.
Extreme Space Weather Event — A rare, high-intensity solar storm capable of causing global impacts.
F
F-region (Ionosphere) — The upper ionosphere layer that allows long-distance radio communication.
Far-side Imaging — Indirect methods of detecting activity on the far side of the Sun.
Filament — A long structure of cool, dense plasma suspended in the corona by magnetic fields.
Flare — A sudden release of energy on the Sun producing intense radiation.
Flare Ribbon — Bright regions on the Sun’s surface marking where magnetic energy is released during a flare.
Flux Rope — A twisted bundle of magnetic field lines, often at the core of CMEs.
Footpoint — The location where a magnetic loop or flux tube connects to the surface.
Forbush Decrease — A temporary drop in cosmic-ray intensity caused by passing solar disturbances.
Free Magnetic Energy — Energy stored in stressed magnetic fields that can power eruptions.
G
G-class Geomagnetic Storm — A storm graded from G1 to G5 on NOAA’s geomagnetic scale.
Galactic Cosmic Rays (GCRs) — High-energy particles originating outside the solar system.
Gamma Rays — The most energetic form of light, produced in strong flares and particle interactions.
Gauss — A unit used to measure magnetic-field strength.
Geoeffective — A solar event likely to affect Earth’s magnetic environment.
Geomagnetic Storm — A disturbance in Earth’s magnetosphere driven by solar wind or CMEs.
Gradual SEP Event — A particle event accelerated mainly by CME-driven shocks.
Granulation — The cellular pattern on the solar surface caused by convection.
GLE — Ground Level Enhancement — A rare solar particle event strong enough for particles to reach Earth’s surface detectors.
H
H-alpha — A specific red wavelength of hydrogen light used to view filaments and chromospheric activity.
Heliographic Latitude/Longitude — The coordinate system used to map positions on the Sun.
Heliopause — The outer boundary of the heliosphere where the solar wind gives way to interstellar space.
Heliophysics — The study of the Sun, the solar wind, and how solar activity interacts with planets and space environments.
Heliosphere — The vast bubble of solar wind and magnetic field surrounding the Sun and all the planets.
Helioseismology — The study of sound waves inside the Sun to learn about its interior structure.
HCS — Heliospheric Current Sheet — A giant, wavy surface in the heliosphere where the Sun’s magnetic polarity flips.
HMF — Heliospheric Magnetic Field — The magnetic field carried outward by the solar wind.
HSS — High-Speed Stream — Fast solar wind flowing from a coronal hole.
I
IBEX — Interstellar Boundary Explorer — A mission that maps the outer heliosphere using energetic neutral atoms.
ICME — Interplanetary CME — A coronal mass ejection that has traveled into the heliosphere.
Ionosphere — The charged layer of Earth’s upper atmosphere affected strongly by solar radiation.
IMF — Interplanetary Magnetic Field — The Sun’s magnetic field stretched out into space by the solar wind.
IMF Sector Boundary — The region where the magnetic field direction switches polarity in the solar wind.
IMAP — Interstellar Mapping and Acceleration Probe — An upcoming mission to study the heliosphere’s boundary.
Interchange Reconnection — Magnetic reconnection between open and closed magnetic field lines.
Interplanetary Shock — A shock wave traveling through the solar wind, often driven by CMEs or HSSs.
Interstellar Medium (ISM) — The gas, dust, and plasma between stars.
J
Jet — Jet-like Eruption — A narrow burst of plasma ejected from the solar atmosphere.
Joule Heating — Energy deposited into a planet’s atmosphere when currents flow during geomagnetic storms.
Jupiter’s Aurora — Intense auroras produced by Jupiter’s strong magnetic field and interactions with its moons.
K
Kp Index — A global measure of geomagnetic storm activity on a scale from 0 to 9.
Kelvin–Helmholtz Waves — Waves formed at the boundary between two flowing plasmas, such as the solar wind and magnetosphere.
Kinetic Energy Spectrum — The distribution of particle energies measured in the solar wind or SEP events.
L
L1 — First Lagrange Point — A gravitationally stable point between Earth and the Sun used for solar-wind monitoring.
L2 — Second Lagrange Point — A point behind Earth used for some solar imagers and space telescopes.
Langmuir Waves — Plasma oscillations caused by electron motion in the solar wind.
LASCO — Large Angle and Spectrometric Coronagraph — SOHO’s instrument that reveals CMEs by blocking the Sun’s disk.
Limb (Solar Limb) — The visible edge of the Sun’s disk.
Light Curve — A plot of brightness over time, often used for flares.
Lyman-alpha — A UV hydrogen line used to study the chromosphere and solar irradiance.
M
Magnetogram — An image showing the strength and polarity of magnetic fields on the Sun’s surface.
Magnetic Cloud — A smooth, rotating magnetic structure inside an ICME.
Magnetic Reconnection — The process where magnetic field lines break and reconnect, releasing energy.
Magnetopause — The boundary between Earth’s magnetosphere and the solar wind.
Magnetosphere — The region around a planet dominated by its magnetic field.
Magnetosheath — The turbulent region of shocked solar wind just outside the magnetopause.
Major Flare — An M-class or X-class solar flare.
MHD — Magnetohydrodynamics — The physics of plasma treated as a fluid interacting with magnetic fields.
MHD Wave — A wave in a magnetised plasma, such as Alfvén or fast-mode waves.
Magnetic Flux Tube — A bundle of magnetic field lines guiding plasma motion.
N
Neutral Line — A boundary on the Sun where magnetic polarity changes direction.
Neutral Sheet — The extended heliospheric surface where the IMF polarity flips (part of the current sheet).
Neutron Monitor — A ground-based detector that measures cosmic rays and GLEs.
Nonthermal Emission — Radiation produced by accelerated particles rather than heat.
North–South Asymmetry — Uneven solar activity between the Sun’s hemispheres.
Nuclear Gamma-Ray Line — A gamma-ray signature produced by nuclear reactions in strong solar flares.
Null Point (Magnetic) — A spot where magnetic field strength drops to zero, often a reconnection site.
O
Open Magnetic Field — A magnetic field line that extends outward into the heliosphere instead of looping back to the Sun.
Optical Depth — A measure of how transparent or opaque a medium is to light.
Optically Thin Plasma — Plasma that allows most radiation to pass through without being absorbed.
Outflow Region — The area where plasma escapes upward during reconnection or eruptions.
P
Parker Spiral — The spiral shape of the heliospheric magnetic field caused by the Sun’s rotation.
Parker Solar Probe — A NASA mission flying into the Sun’s corona to sample the solar wind at its origin.
Penumbra — The outer, filamentary region of a sunspot.
Perihelion — The point in a spacecraft or planet’s orbit closest to the Sun.
Photosphere — The visible surface of the Sun where most sunlight originates.
PIC Model (Particle-in-Cell) — A simulation technique that tracks plasma by following charged particles directly.
Plage — Bright chromospheric areas associated with strong magnetic fields.
Plasma — Ionized gas that responds to electric and magnetic fields, making up the Sun and solar wind.
Plasma Beta — The ratio of gas pressure to magnetic pressure in a plasma.
Polar Field Reversal — The flipping of the Sun’s magnetic poles every ~11 years.
Polarity Inversion Line (PIL) — A boundary on the solar surface where magnetic polarity changes sign.
Prominence — A large loop or sheet of cooler plasma suspended in the corona by magnetic fields.
Proton Flux — The number of energetic protons detected per second, used to track SEP events.
Q
Quasi-Parallel Shock — A CME shock where the magnetic field runs roughly parallel to the shock front.
Quasi-Perpendicular Shock — A shock where the magnetic field is nearly perpendicular to the shock surface.
Quiet Sun — Regions of the solar surface not actively producing flares, sunspots, or strong magnetic activity.
Quiescent Filament — A long-lasting, stable filament that may persist for weeks before erupting.
R
Radiative Zone — The region inside the Sun where energy moves outward mainly by radiation.
Radio Burst — A sudden increase in radio emission from the Sun during flares or shocks.
Reconnection Jet — A fast burst of plasma expelled during magnetic reconnection.
Redshift/Blueshift — Changes in wavelength that reveal motion toward or away from the observer.
Rope-like CME — A CME with a distinct flux-rope magnetic structure.
S
Sector Boundary — A region in the solar wind where the magnetic polarity flips.
SEP — Solar Energetic Particles — Fast ions and electrons accelerated by flares or CME-driven shocks.
SEP Event — A rise in energetic particle flux measured by spacecraft or ground detectors.
Sheath Region — The turbulent compressed plasma between a CME’s shock and its magnetic cloud
.
Shock Front — A boundary where solar-wind plasma is suddenly compressed and heated.
Slow Solar Wind — A slower stream of solar wind, typically originating from closed-field regions.
Solar Cycle — The roughly 11-year rise and fall of solar magnetic activity.
Solar Flare — A sudden burst of energy and radiation from the Sun’s atmosphere.
Solar Maximum — The peak of the solar cycle, when sunspots and flares are most frequent.
Solar Minimum — The quiet part of the solar cycle with fewer active regions.
Solar Orbiter — An ESA/NASA mission studying the Sun up close and from out-of-equatorial latitudes.
Solar Radio Blackout — A loss of communication caused by intense ionospheric absorption from X-rays.
Solar Wind — A continuous flow of charged particles streaming outward from the Sun.
Space Weather — The conditions in space influenced by solar activity and their effects on technology and planets.
Spicules — Thin, jet-like plasma structures rising from the chromosphere.
SSN — Sunspot Number — A daily measure of how many sunspots or groups are visible on the Sun.
Substorm — A short, explosive disturbance in Earth’s magnetosphere that intensifies auroras.
Superflare — An extremely large flare observed on some stars, far stronger than typical solar flares.
Switchback — A sudden reversal in the solar-wind magnetic field direction, seen by Parker Solar Probe.
Synoptic Map — A global map of solar magnetic fields created over a full rotation.
T
Tachocline — The thin transition layer between the Sun’s radiative zone and convection zone where strong shear helps generate the solar magnetic field.
Thermosphere — The upper layer of Earth’s atmosphere strongly affected by solar EUV and particle input.
Toroidal Field — Magnetic field wrapped around the Sun’s rotation axis, important in the solar cycle.
Transition Region — The thin layer between the chromosphere and corona where temperature rises sharply.
Transients (Solar Wind) — Short-lived disturbances such as CMEs or shocks moving through the solar wind.
Type II Radio Burst — A slowly drifting radio signal produced by a CME-driven shock.
Type III Radio Burst — A fast-drifting radio signature caused by energetic electrons streaming along magnetic field lines.
U
Ultraviolet (UV) — A wavelength range used to study the Sun’s atmosphere and flares.
Umbra — The dark central region of a sunspot.
Ulysses (Mission) — A joint ESA/NASA mission that studied the high-latitude solar wind and polar magnetic field.
V
Van Allen Belts — Rings of trapped charged particles surrounding Earth.
W
Waves (MHD) — Disturbances in magnetised plasma, including Alfvén, slow, and fast-mode waves.
Wavelength — The distance between peaks of a wave, used to distinguish types of solar radiation.
WIND (Mission) — A NASA spacecraft measuring solar wind, particles, and magnetic fields since 1994.
X
X-class Flare — The most powerful class of solar flare measured by GOES X-ray flux.
X-point — A location where magnetic field lines cross and reconnection can occur.
X-ray Emission — High-energy radiation produced during flares and in hot coronal plasma.
Y
Yohkoh (Mission) — A Japanese mission that provided groundbreaking X-ray observations of solar flares and the corona.
Young Active Stars — Stars with strong magnetic activity and intense space weather that affect exoplanet habitability.
Z
Zeeman Effect — The splitting of spectral lines in a magnetic field, used to measure solar magnetism.
Zonal Flow — Large-scale east–west flows in the Sun linked to the solar cycle.