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.
Aurora
The aurora (borealis in the north, australis in the south) is a natural light display caused by charged particles from the solar wind colliding with gases in Earth's upper atmosphere. Earth's magnetic field channels these particles toward the polar regions, where they collide with oxygen and nitrogen atoms, exciting them and causing them to emit light as they return to their normal state.
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.