Space Weather
Solar storms, the solar wind, and their effects near Earth.
Overview
Space weather describes conditions driven by the Sun — the solar wind, flares and coronal mass ejections — and their effects on Earth's magnetosphere, on satellites, on power grids, and on the aurorae. It is the one branch of astronomy with routine operational consequences on the ground.
- Flares travel at light speed and arrive in about 8 minutes; coronal mass ejections take one to three days.
- Aurorae are caused by particles guided along magnetic field lines into the upper atmosphere, not by the particles arriving directly.
- The 1859 Carrington event is the reference case for how severe a storm can be.
- Forecast lead time is short — hours to a few days — and the uncertainty is large.
What the Sun sends
- The solar wind: a continuous outflow of charged particles from the corona, varying in speed and density, which shapes Earth's magnetosphere continuously.
- Solar flares: sudden releases of magnetic energy producing intense electromagnetic radiation across the spectrum. Because it is light, it arrives in about eight minutes and can disrupt radio communication on the sunlit side almost immediately.
- Coronal mass ejections: enormous eruptions of plasma and embedded magnetic field. These are the main driver of severe geomagnetic storms and take roughly one to three days to reach Earth.
- Solar energetic particles: high-energy particles accelerated by flares and CME shocks, which can reach Earth within tens of minutes and pose a radiation hazard to spacecraft and to crews outside the magnetosphere.
How aurorae actually form
The common description — particles from the Sun hitting the atmosphere — is close enough to be memorable and wrong in an important detail. Solar wind particles are largely deflected by Earth's magnetosphere. What actually produces an aurora is energy transferred into the magnetosphere, which accelerates particles already present there down magnetic field lines into the upper atmosphere near the poles.
Those particles excite atmospheric atoms and molecules, which then emit at characteristic wavelengths: atomic oxygen produces the familiar green at around 100 to 200 kilometres and a rarer deep red at higher altitude, while nitrogen contributes blue and purple. The colours are emission lines, which is why aurora photographs show discrete hues rather than a continuous spectrum.
Effects that matter operationally
Geomagnetic storms induce currents in long conductors on the ground. In March 1989 a storm caused a transformer failure cascade that blacked out the Hydro-Québec grid within minutes, and long pipelines experience accelerated corrosion from the same mechanism.
Satellites face several distinct hazards: radiation damage and single-event upsets in electronics, charging of spacecraft surfaces, and increased atmospheric drag as the upper atmosphere heats and expands during storms — which measurably lowers orbits and has caused loss of newly launched satellites. High-frequency radio and satellite navigation both degrade during ionospheric disturbances, and airlines reroute polar flights during major events.
Forecasting, and its limits
Space weather forecasting is genuinely difficult. A coronal mass ejection's effect depends heavily on the orientation of its embedded magnetic field, which cannot be reliably determined until it reaches spacecraft at the L1 point roughly 1.5 million kilometres upstream — giving perhaps 15 to 60 minutes of definite warning before arrival at Earth.
The Carrington event of 1859 remains the benchmark for severity: aurorae were reported at tropical latitudes and telegraph systems failed, in some cases operating on induced current alone. A comparable event today would affect infrastructure that did not exist in 1859, which is why operational forecasting centres exist at all. Asteria Star does not publish simulated conditions; current values come from official forecasting sources or are not shown.
Continue in the data
Catalogues, hubs, and reference pages that hold the underlying records for this topic.
Frequently asked
- How long does it take for a solar storm to reach Earth?
- It depends on what is travelling. A flare's electromagnetic radiation arrives in about eight minutes, at light speed. Solar energetic particles can arrive within tens of minutes. A coronal mass ejection — the plasma cloud that drives major geomagnetic storms — typically takes one to three days.
- What causes the aurora?
- Energy from the solar wind transferred into Earth's magnetosphere, which accelerates charged particles along magnetic field lines into the upper atmosphere near the poles. Those particles excite oxygen and nitrogen, which emit at specific wavelengths — green and deep red from oxygen, blue and purple from nitrogen. Solar particles do not mostly strike the atmosphere directly.
- Can a solar storm damage power grids?
- Yes. Geomagnetic storms induce currents in long conductors, including transmission lines, which can drive transformers into saturation and cause cascading failures. The March 1989 storm blacked out the Hydro-Québec grid in minutes. Severe events also accelerate corrosion in pipelines through the same induction mechanism.
- How much warning is there before a geomagnetic storm?
- Typically one to three days from observing a coronal mass ejection leave the Sun, but the crucial detail — the orientation of its magnetic field, which largely determines severity — is not reliably known until the cloud reaches monitoring spacecraft about 1.5 million kilometres upstream. That gives roughly 15 to 60 minutes of definite warning.