Education Center
Learn Space Weather
Plain-English explanations of every concept behind the live data on this site — what each metric means, why it matters, and how scientists actually measure it.
What Is Space Weather?
Space weather is the set of constantly changing conditions in the space surrounding Earth, driven almost entirely by activity on the Sun. Just as terrestrial weather describes the state of Earth's atmosphere — wind, rain, storms — space weather describes the state of the plasma, magnetic fields, and radiation filling the roughly 150-million-kilometer gap between the Sun and Earth. The Sun is not a quiet, unchanging light bulb. It's a churning ball of superheated plasma with a powerful, constantly shifting magnetic field, and its outer atmosphere (the corona) is so hot — over a million degrees Celsius — that it can't be gravitationally contained. It boils off into space as a continuous outward stream of charged particles called the solar wind, blowing outward in every direction at roughly 300-800 kilometers per second. Layered on top of that steady background wind, the Sun periodically erupts: solar flares release sudden, intense bursts of electromagnetic radiation, and coronal mass ejections (CMEs) hurl billion-ton clouds of magnetized plasma outward at speeds that can exceed 2,000 kilometers per second. Earth isn't a passive bystander to any of this. Our planet is wrapped in its own protective magnetic field — the magnetosphere — generated by convective currents in Earth's molten outer core. Most of the time, this magnetic shield does its job quietly, deflecting the solar wind around the planet the way a rock in a stream diverts water around it. But when the incoming solar wind's own magnetic field happens to point south (the opposite direction to Earth's field near the equator), the two fields can link together in a process called magnetic reconnection, opening a temporary pathway for solar wind energy and particles to pour directly into Earth's magnetic environment. When that happens — especially during a fast, dense CME impact with a strongly southward field — the result is a geomagnetic storm: a measurable, sometimes dramatic disturbance of Earth's magnetic field that can last anywhere from hours to several days. Space weather, in short, is the whole causal chain: what the Sun is doing right now, what's currently traveling through the solar wind toward Earth, and how Earth's magnetosphere and upper atmosphere are responding to it at this moment. Every live number on this website — the Kp index, solar wind speed, IMF Bz and Bt, X-ray flux, proton flux, sunspot number — is a different instrument's view into one piece of that same continuous, real, physical process.
Kp Index
The Kp index is a simple 0-to-9 scale that summarizes how disturbed Earth's magnetic field is at any given time. Instead of asking you to interpret raw magnetometer readings, scientists combine data from observatories around the world into this one number, updated every 3 hours. Think of it like a Richter scale for geomagnetic activity — a bigger number means a bigger disturbance, full stop.
Solar Wind
The solar wind is a continuous stream of charged particles — mostly electrons and protons — that flows outward from the Sun's outer atmosphere (the corona) in every direction, carrying the Sun's magnetic field along with it. It's not an occasional event; it blows constantly, but its speed and density vary a lot depending on conditions on the Sun at the moment that particular stream left.
Bz (IMF Bz)
Bz is the north-south component of the interplanetary magnetic field (IMF) carried by the solar wind, measured in nanotesla (nT). What matters most about Bz isn't its size — it's its sign. Earth's own magnetic field points north near the equator, so when the incoming solar wind's field points south (a negative Bz), the two fields can link together through a process called magnetic reconnection, opening a pathway for solar wind energy to pour into Earth's magnetosphere.
Bt (Total Magnetic Field)
Bt is the total strength of the interplanetary magnetic field, combining all three of its directional components (Bx, By, and Bz) into one overall magnitude, measured in nanotesla (nT). Where Bz tells you which way the field is pointing, Bt tells you how strong it is overall, calculated as the square root of the sum of each component squared.
Interplanetary Magnetic Field (IMF)
The interplanetary magnetic field (IMF) is the Sun's own magnetic field, stretched out and carried through the solar system by the solar wind. As the Sun rotates, this field twists into a spiral shape (the Parker spiral), and by the time it reaches Earth it's a tangled but measurable field with three directional components — Bx, By, and Bz — plus a total strength, Bt.
Solar Flares
A solar flare is a sudden, intense burst of radiation released when magnetic energy that has built up in the Sun's atmosphere is abruptly released, usually near sunspot groups where magnetic field lines have become twisted and tangled. Flares release energy across the entire electromagnetic spectrum, from radio waves to X-rays and gamma rays, all essentially simultaneously.
Coronal Mass Ejections (CMEs)
A coronal mass ejection (CME) is a massive burst of plasma and magnetic field launched from the Sun's corona into space, often (but not always) associated with a large solar flare. Unlike the constant solar wind, a CME is a distinct, one-time event — essentially a giant cloud of solar material hurled outward, which can be Earth-directed or aimed elsewhere entirely.
Coronal Holes
A coronal hole is a region of the Sun's corona where the magnetic field lines are "open" — extending out into space rather than looping back to the Sun's surface. Because there's less dense plasma trapped there, coronal holes appear as dark patches in extreme ultraviolet and X-ray images of the Sun, even though they're not physically empty holes.
The Aurora (Northern & Southern Lights)
The aurora borealis and aurora australis are dynamic atmospheric light displays triggered by solar activity. The phenomenon originates when high-speed solar wind streams, solar flares, or Coronal Mass Ejections (CMEs) launch charged electrons and protons from the Sun's corona into interplanetary space. Traveling at millions of miles per hour, these particles collide with Earth's protective magnetosphere boundary at the L1 compression threshold. When the Interplanetary Magnetic Field (Bz) tilts deeply Southward, magnetic reconnection occurs, creating a partial breach in Earth's magnetic shield. These energetic particles channel directly down Earth's dipole magnetic field lines into the upper ionosphere, concentrating around the permanent auroral oval boundaries at the high latitudes. As these solar electrons collide with atmospheric gases between 60 and 200 miles high, they excite the atoms. When returning to their baseline energy states, they release photons of light. Low-altitude oxygen atom collisions generate the classic vivid emerald-green curtains, while rarer high-altitude oxygen atomic interactions emit striking deep crimson red curtains. Molecular nitrogen collisions ignite brilliant pink borders, deep blues, and structural violet wave edges. Observing these dynamic displays requires checking the planetary Kp Index, local weather cloud cover metrics, lunar phase illumination percentages, and finding dark skies away from light pollution around local magnetic midnight.
Proton Flux
Proton flux measures how many high-energy protons (specifically ≥10 MeV, energetic enough to penetrate spacecraft shielding) are arriving from the Sun, in particle flux units (pfu). Large flares and CMEs can accelerate protons to these energies, and a proton event typically follows a major flare by tens of minutes to a few hours.
Electron Flux
Electron flux measures the number of high-energy electrons arriving at a given point, similar in concept to proton flux but tracking electrons instead. These "killer electrons" are often associated with Earth's radiation belts (the Van Allen belts) and can become significantly more energetic and numerous during geomagnetic storms.
X-ray Flux
X-ray flux measures the intensity of X-rays reaching Earth from the Sun, in watts per square meter (W/m²), continuously monitored by GOES satellites. It's the raw measurement behind the familiar A/B/C/M/X solar flare letter scale — each letter represents a tenfold jump in flux.
Sunspots
Sunspots are temporary dark patches on the Sun's visible surface, caused by concentrated magnetic field lines that locally suppress heat flow, making them appear cooler (and thus darker) than the surrounding surface — though they're still extremely hot in absolute terms. The sunspot number is a standardized monthly count of sunspots and sunspot groups, tracked continuously since the mid-1700s.
Solar Cycle
The solar cycle is the Sun's roughly 11-year pattern of rising and falling magnetic activity, driven by the gradual reversal of the Sun's magnetic field. It swings between solar minimum (few sunspots, fewer flares, generally quiet) and solar maximum (many sunspots, frequent flares and CMEs, and the best odds of strong geomagnetic storms and aurora).
F10.7 Solar Radio Flux
The F10.7 index measures the intensity of radio emissions from the Sun at a wavelength of 10.7 centimeters, in solar flux units (sfu). Unlike the sunspot number, which relies on visual counting, F10.7 is a direct physical radio measurement — and the two track each other closely, making F10.7 a valuable independent cross-check on overall solar activity.
The Sun
The Sun is a G-type main-sequence star, a massive sphere of plasma held together by its own gravity and powered by nuclear fusion at its core. At the core, temperatures near 15 million Kelvin and immense pressure fuse hydrogen nuclei into helium, releasing energy as gamma rays. That energy doesn't escape instantly — it undergoes a slow random-walk diffusion through the dense radiative zone, typically taking over 100,000 years to reach the surface, before finally radiating into space as sunlight in about 8.3 minutes of travel time to Earth. The Sun's visible surface, the photosphere, sits at roughly 5,500°C, while the wispy outer corona above it is paradoxically far hotter, reaching over a million degrees — a genuine unsolved problem in solar physics known as the coronal heating problem. The Sun's magnetic field, generated by convective plasma motion inside the star, drives an 11-year solar cycle of rising and falling activity, during which sunspots, solar flares, and coronal mass ejections become more or less frequent. These eruptions launch charged particles and radiation toward Earth, forming the basis of space weather. The Sun accounts for over 99.8% of the solar system's total mass and has been fusing hydrogen for about 4.6 billion years, with roughly another 5 billion years of hydrogen fuel remaining before it evolves into a red giant.
The Moon
The Moon is Earth's only natural satellite, most likely formed roughly 4.5 billion years ago when a Mars-sized body, sometimes called Theia, collided with the early Earth, ejecting debris that coalesced into the Moon we see today. It orbits Earth at an average distance of about 384,400 km, completing one orbit roughly every 27.3 days. The Moon is tidally locked to Earth — its rotation period exactly matches its orbital period — which is why the same hemisphere always faces us, while the far side remains permanently hidden from direct view. Its surface is dominated by two terrains: bright, heavily cratered highlands, and darker, smoother maria (Latin for 'seas'), which are actually ancient basaltic lava plains formed by volcanic eruptions billions of years ago. The Moon has no atmosphere and negligible magnetic field, leaving its surface directly exposed to solar wind and micrometeorite impacts. Its gravity is the dominant driver of Earth's ocean tides, and its own gravitational pull is gradually slowing Earth's rotation while the Moon itself slowly drifts away at about 3.8 centimeters per year. For skywatchers, lunar brightness is a major practical factor — a full moon can wash out faint aurora and deep-sky objects, while a new moon offers the darkest skies for observation.
Black Holes
A black hole is a region of spacetime where gravity is so intense that nothing, not even light, can escape once it crosses the event horizon — the boundary marking the point of no return. Black holes form when sufficiently massive objects collapse under their own gravity. Stellar-mass black holes, typically a few to tens of times the Sun's mass, form when a massive star exhausts its nuclear fuel and its core collapses at the end of a supernova explosion. Supermassive black holes, millions to billions of times the Sun's mass, reside at the centers of most large galaxies, including the Milky Way's own Sagittarius A*, though how they grew so large remains an active area of research. Near a black hole, gravity bends the path of light itself, a phenomenon called gravitational lensing, which can distort or magnify the appearance of background objects and produces the characteristic bright, warped 'photon ring' seen in simulations and the real Event Horizon Telescope images. Matter falling toward a black hole often forms a swirling, superheated accretion disk, which can glow brightly across the electromagnetic spectrum before crossing the event horizon. Despite popular imagination, black holes don't 'suck in' everything nearby — an object orbiting at a safe distance behaves according to ordinary gravity, just as it would around any other mass of the same size.
Earth & Magnetosphere
Earth is the third planet from the Sun and the only known world with liquid water on its surface and life. Beneath the surface, a solid inner core and molten outer core generate Earth's magnetic field through a process called the geodynamo: convective motion of electrically conductive molten iron, combined with Earth's rotation, sustains a self-reinforcing magnetic field that extends far into space. This field creates the magnetosphere, a protective bubble that deflects most of the charged particles streaming from the Sun as solar wind. On the sunward side, the magnetosphere is compressed to roughly 10 Earth radii by solar wind pressure, while on the night side it stretches into a long magnetotail extending hundreds of Earth radii into space. Two doughnut-shaped regions of trapped high-energy particles, the Van Allen radiation belts, orbit within the inner magnetosphere. When solar wind conditions are calm, the magnetosphere efficiently shields Earth's surface and atmosphere from most incoming radiation. But when the interplanetary magnetic field carried by the solar wind points southward, it can partially connect with Earth's own northward-pointing field lines through a process called magnetic reconnection, opening a temporary channel that lets solar wind energy and particles flow into the upper atmosphere — the same process responsible for the aurora, and for the disruptions grouped together as space weather.
The Solar System
The solar system formed roughly 4.6 billion years ago from the gravitational collapse of a giant molecular cloud, most of which condensed into the Sun while the remaining material flattened into a rotating protoplanetary disk that eventually assembled into planets, moons, and smaller bodies. The four inner, rocky terrestrial planets — Mercury, Venus, Earth, and Mars — orbit closest to the Sun, composed mainly of rock and metal. Beyond them lie the four outer giant planets: Jupiter and Saturn, gas giants dominated by hydrogen and helium, and Uranus and Neptune, often classified separately as ice giants for their higher proportion of water, ammonia, and methane ices. Between Mars and Jupiter lies the asteroid belt, a region of rocky leftover planetesimals that never coalesced into a full planet, likely due to Jupiter's disruptive gravitational influence. Beyond Neptune's orbit lies the Kuiper Belt, a disk of icy bodies including the dwarf planet Pluto, and much farther out, the theorized Oort Cloud is thought to be the source of long-period comets, extending perhaps halfway to the nearest star. The Sun's influence doesn't end abruptly — the heliosphere, a vast bubble inflated by the solar wind, extends far past Pluto's orbit until it meets the pressure of the interstellar medium at the heliopause, which NASA's Voyager 1 spacecraft crossed into true interstellar space in 2012.
Stars & Stellar Evolution
Stars are born inside nebulae, vast clouds of gas and dust where gravity slowly pulls denser pockets of material together. As a collapsing cloud fragment contracts under its own gravity, it heats up, eventually reaching temperatures and pressures in its core high enough to ignite nuclear fusion — the process that defines a true star. For the vast majority of a star's life, it sits on the main sequence, steadily fusing hydrogen into helium in its core and radiating the resulting energy as light and heat; our own Sun is roughly midway through its roughly 10-billion-year main-sequence lifetime. A star's ultimate fate depends almost entirely on its mass. Lower-mass stars like the Sun eventually exhaust their core hydrogen, swell into a red giant, then gently shed their outer layers to form a glowing planetary nebula, leaving behind a slowly cooling white dwarf remnant. Far more massive stars burn through their fuel much faster and end their lives in a catastrophic supernova explosion, which can leave behind an ultra-dense neutron star or, for the most massive stars, collapse further into a stellar-mass black hole. These supernova explosions are also how the universe's heavier elements — including much of the carbon, oxygen, and iron that make up planets and life — are forged and scattered into space, seeding future generations of stars and planets.
Galaxies & Nebulas
A galaxy is a massive, gravitationally bound collection of stars, gas, dust, and dark matter, ranging from small dwarf galaxies with a few million stars to giant ellipticals with trillions. Galaxies are broadly classified into three main shapes: spiral galaxies, with a flattened, rotating disk and sweeping arms of young stars; elliptical galaxies, smooth and roughly spherical or oval, generally with older stellar populations; and irregular galaxies, which lack a defined symmetric structure. Our own Milky Way is a barred spiral galaxy, estimated to hold somewhere between 100 and 400 billion stars, with our solar system located in one of its spiral arms roughly 26,000 light-years from the galactic center. Nebulas, by contrast, are vast interstellar clouds of gas and dust rather than collections of stars. Some, like the famous Orion Nebula, are stellar nurseries where gravity is actively collapsing gas into new stars. Others are the remnants of stellar death — a planetary nebula forms when a dying Sun-like star sheds its outer layers, while a supernova remnant is the expanding debris from a massive star's explosive end. Galaxies themselves don't hold together on visible matter alone: their rotation speeds and gravitational interactions require far more mass than can be accounted for by stars and gas, evidence for dark matter, an invisible form of matter that doesn't emit or absorb light but whose gravity is essential to how galaxies form and hold together.
Eclipses (Solar & Lunar)
An eclipse occurs when the Sun, Earth, and Moon align closely enough for one body's shadow to fall on another — an alignment astronomers call syzygy. A solar eclipse happens at new moon, when the Moon passes directly between the Sun and Earth, casting its shadow onto Earth's surface. This doesn't happen every new moon because the Moon's orbit is tilted about 5 degrees relative to Earth's orbital plane, so precise alignment only occurs a few times a year. The Moon's shadow has two parts: the umbra, a narrow, fully-shadowed cone where observers see a total eclipse, and the surrounding penumbra, where only a partial eclipse is visible. Because the umbra is only about 100-160 km wide, total solar eclipses are visible only along a narrow path of totality, while a much wider region experiences a partial eclipse. Just before and after totality, sunlight streaming through valleys on the Moon's jagged limb can produce a brief, striking effect called Baily's beads. A lunar eclipse works differently: it happens at full moon, when Earth passes directly between the Sun and Moon, casting Earth's own shadow onto the lunar surface. Because Earth's shadow is much larger than the Moon, and because the Moon can pass through Earth's outer penumbra and inner umbra, lunar eclipses are visible from the entire night side of Earth at once, and often display a striking reddish 'blood moon' color as sunlight filters through Earth's atmosphere and bends into the shadow.
Comets
A comet is a small icy body — often described as a 'dirty snowball' of frozen water, carbon dioxide, ammonia, and rocky dust — that spends most of its life in the cold outer reaches of the solar system. As a comet's highly elliptical orbit carries it closer to the Sun, solar heating causes its frozen volatiles to sublimate directly from solid to gas, releasing dust and gas that form a glowing envelope around the nucleus called the coma, often tens of thousands of kilometers across. Solar radiation pressure and the solar wind push this material away from the Sun, producing one or two visible tails: a curved, yellowish dust tail that traces the comet's orbital path, and a straighter, bluish ion tail composed of ionized gas that always points directly away from the Sun regardless of the comet's direction of travel. Short-period comets, with orbits under 200 years, are thought to originate in the Kuiper Belt beyond Neptune; long-period comets, which can take thousands of years to orbit, are believed to come from the far more distant, spherical Oort Cloud. Perhaps the most famous comet, Halley's Comet, returns to the inner solar system roughly every 76 years and was last visible from Earth in 1986, with its next appearance expected around 2061. Each close pass to the Sun strips away some of a comet's material, meaning most comets have a finite lifespan before they eventually fragment or become dormant.
Asteroids
Asteroids are rocky, metallic remnants left over from the solar system's formation roughly 4.6 billion years ago, material that never coalesced into a full planet. The vast majority orbit within the main asteroid belt, a region between Mars and Jupiter, where Jupiter's powerful gravity is thought to have prevented these planetesimals from ever assembling into a single world. Asteroids vary enormously in size and composition — Ceres, the largest object in the belt at roughly 940 km across, is large enough to be classified as a dwarf planet, while most asteroids are far smaller, ranging from boulder-sized fragments to bodies hundreds of kilometers wide. They're broadly grouped by composition into carbon-rich C-type asteroids (the most common), stony S-type asteroids, and metallic M-type asteroids rich in iron and nickel, thought to be remnants of the cores of larger, shattered protoplanets. Asteroids whose orbits bring them within about 1.3 astronomical units of the Sun are classified as Near-Earth Objects (NEOs), and NASA and other space agencies actively track thousands of them to assess any potential impact risk. In a landmark planetary defense test, NASA's DART spacecraft deliberately collided with the small asteroid moonlet Dimorphos in September 2022, successfully altering its orbital period and demonstrating for the first time that a kinetic impact could meaningfully change an asteroid's trajectory — a real, tested strategy for deflecting a future hazardous impactor.
Meteor Showers
A meteor shower occurs when Earth, in its orbit around the Sun, passes through a trail of dust and debris left behind by a comet (or, in rare cases, an asteroid) along its orbital path. As these small particles, most no larger than a grain of sand, slam into Earth's atmosphere at speeds often exceeding 100,000 mph, friction with the air heats and vaporizes them almost instantly, producing the brief, glowing streaks known as meteors, or more casually, shooting stars. Because all the debris in a given trail is moving roughly parallel through space, the resulting meteors appear to radiate outward from a single point in the sky, called the radiant, typically located in the constellation for which the shower is named — the Perseids appear to radiate from Perseus, the Geminids from Gemini. Meteor shower intensity is measured using the Zenithal Hourly Rate (ZHR), an estimate of how many meteors a single observer could see per hour under ideal dark-sky conditions with the radiant directly overhead — actual visible rates are almost always lower due to light pollution, moonlight, or a radiant that hasn't yet risen high in the sky. Some of the most reliable annual showers include the Perseids, peaking in mid-August and associated with Comet Swift-Tuttle, and the Geminids, peaking in mid-December and unusually linked to a rocky asteroid, 3200 Phaethon, rather than an icy comet — a genuine astronomical oddity researchers still study to understand how an asteroid can shed a comet-like debris trail.
Satellites & Spacecraft
Thousands of active satellites currently orbit Earth, generally grouped by altitude into three main regions: low Earth orbit (LEO), typically a few hundred to about 2,000 km up, home to the International Space Station and most modern communication constellations like Starlink; medium Earth orbit (MEO), where GPS and other navigation satellites operate at roughly 20,000 km; and geostationary orbit (GEO), a precise altitude of about 35,786 km where a satellite's orbital period exactly matches Earth's rotation, letting it appear fixed over one point on the globe — ideal for weather and communications satellites. Space weather poses real, practical risks to this infrastructure. During geomagnetic storms, Earth's upper atmosphere heats and expands, increasing atmospheric density at low-Earth-orbit altitudes and creating extra drag that can degrade a satellite's orbit faster than expected, sometimes requiring emergency correction maneuvers. A dedicated fleet of spacecraft exists specifically to monitor these conditions: NOAA's DSCOVR satellite sits at the L1 Lagrange point, about 1.5 million km sunward of Earth, providing roughly 15-60 minutes of advance warning before incoming solar wind and CMEs arrive; NASA's SDO continuously images the Sun to track flares and active regions; and NASA's twin Voyager probes, launched in 1977, have long since left the solar system entirely — Voyager 1 crossed into true interstellar space in 2012, making it the most distant human-made object ever built, still transmitting data across billions of kilometers using a plutonium power source expected to last into the 2020s and beyond.
Stargazing & Astrophotography
Stargazing is the observational practice of viewing celestial objects with the naked eye, binoculars, or a telescope, and can range from simply learning constellations to serious deep-sky astrophotography. Telescopes fall into two main optical designs: refracting telescopes, which use a glass lens at the front to bend and focus light, and reflecting telescopes, which use a curved mirror instead — reflectors generally offer more aperture (light-gathering power) per dollar, while refractors tend to need less maintenance. Beyond the telescope itself, successful observing depends heavily on conditions: light pollution is measured using the Bortle scale, a 1-to-9 rating where 1 represents a pristine, pitch-black rural sky and 9 represents an inner-city sky where only the Moon and brightest planets are visible. Astronomical 'seeing' refers to atmospheric turbulence that causes stars to twinkle and blurs fine telescopic detail, distinct from transparency (which relates to cloud cover and haziness) — both matter for planning a session. For astrophotography specifically, capturing faint, dim objects generally requires a sturdy tripod, a camera capable of long-exposure manual control, and often a delayed shutter release or remote trigger to eliminate camera shake, since even a slight vibration can blur a multi-second exposure. Modern smartphones with dedicated night modes have made basic astrophotography — particularly of bright targets like the Moon or an active aurora — accessible without specialized equipment, though deep-sky targets like nebulae and galaxies still generally require a telescope and dedicated camera setup.