Space Weather
Conditions in the space around Earth, measured now — the geomagnetic index, the solar wind arriving from the Sun, and whether tonight is worth watching for aurora.
Updated moments ago
Quiet
The magnetic field is settled. No aurora outside the polar regions.
Three-hour period beginning 18 Sep, 21:00 UTCS — none
G — none
The last 24 hours
Each bar is one three-hour Kp period, oldest on the left.
Three-day outlook
| Date | Radio blackout (R) | Radiation storm (S) | Geomagnetic storm (G) |
|---|---|---|---|
| 2026-09-19 | None minor 1% |
None 1% |
None |
| 2026-09-20 | None minor 1% |
None 1% |
None |
| 2026-09-21 | None minor 1% |
None 1% |
None |
Recent NOAA notices
What these numbers actually mean
The Kp index
Kp is a single number from 0 to 9 describing how disturbed Earth's magnetic field has been over a three-hour window, averaged across a network of ground magnetometers. It is logarithmic: the jump from Kp 7 to Kp 8 represents far more energy than the jump from Kp 1 to Kp 2. From Kp 5 upward NOAA also labels the event on the G scale, so Kp 5 is G1, Kp 6 is G2, and so on to G5 at Kp 9.
Which Kp you need for aurora
There is no universal threshold — it depends entirely on how far north or south you live.
| Kp | Storm level | Aurora typically reaches |
|---|---|---|
| 3–4 | Unsettled / active | Tromsø, Iceland, Fairbanks, Yellowknife |
| 5 | G1 minor | Northern Scotland, Oslo, Stockholm, the northern US border states |
| 6 | G2 moderate | Northern England, Denmark, New York, Idaho |
| 7 | G3 strong | Southern England, northern Germany, Oregon, Illinois |
| 8–9 | G4–G5 severe to extreme | Central Europe, southern US states — a few times per solar cycle |
Two things ruin an otherwise good forecast: cloud, and the Moon. A high Kp under a full Moon still shows aurora, but the faint structure that makes it worth the drive is lost.
Bz, and why it matters more than the Kp forecast
Bz is the north–south component of the magnetic field carried by the solar wind. When it points north it simply slides past Earth. When it points south — a negative number here — it is anti-parallel to Earth's own field, the two reconnect, and energy pours into the magnetosphere. A sustained Bz around −10 nT or lower, particularly with a solar wind speed above 500 km/s, is the best short-notice aurora signal there is. It also gives you only 15 to 45 minutes of warning, which is why aurora hunters watch this number rather than the daily forecast.
Solar flare classes
Flares are graded by peak X-ray brightness: A, B, C, M and X, each class ten times the one before, with a number giving the position within the class. A C1 is unremarkable. An M5 can black out high-frequency radio on the sunlit side of Earth for tens of minutes. X-class flares are the ones that make the news, and the scale does not stop at X9 — the November 2003 event is estimated at around X45.
Flares themselves arrive at the speed of light, in about eight minutes, and affect radio immediately. The aurora comes from something slower: a coronal mass ejection, a cloud of plasma that takes one to three days to cross the distance. That gap is the entire basis of space weather forecasting.
Does any of this affect life on the ground?
Not your health — the atmosphere and magnetic field absorb the radiation, and there is no measurable effect at sea level. What is affected: high-frequency radio used by aviation and shipping, GPS accuracy, satellite drag in low Earth orbit, polar flight routes, and at extreme levels the power grid. The March 1989 storm put Québec's grid out for nine hours. The 1859 Carrington event set telegraph offices on fire, and a repeat is the scenario most space weather planning is built around.
Where to go next
If you are watching for aurora, pair this page with a dark site and dark-adapted eyes — see our guides on protecting your night vision and finding dark sky. Aurora photographs far better than it looks to the eye, so a camera on a tripod is worth bringing even on a modest night; the settings in our night photography guide transfer directly.
Data source: NOAA Space Weather Prediction Center (planetary K-index, ACE/DSCOVR solar wind, GOES X-ray flux, NOAA scales and issued alerts). Figures are cached for 30 minutes; the Kp index itself is published every three hours. StarryDex is not affiliated with NOAA and this page is not an official forecast — for operational use, consult SWPC directly.
