Score Components & Weights
Five factors are measured in real time and combined proportionally. Total weight = 100%. Each factor is normalised to its realistic range before weighting.
The north-south component of the interplanetary magnetic field. Negative Bz (southward) is the most powerful aurora trigger — it opens the magnetosphere to solar wind energy. Score maxes out at Bz ≤ −20 nT.
Faster solar wind carries more energy into the magnetosphere. Normal solar wind travels at 350–500 km/s. Above 700 km/s is excellent for aurora — it significantly amplifies the Bz effect.
The total interplanetary magnetic field strength (Bt). A stronger total field means more stored energy available for aurora activity. High Bt with southward Bz is the ideal combination.
The number of charged particles per cubic centimeter in the solar wind. Higher density increases the pressure on the magnetosphere. A minor factor compared to Bz and speed, but contributes to overall storm intensity.
Local cloud cover is a pure visibility factor — even a KP 9 storm is invisible under solid cloud. 0% cloud = full 10 points. 100% cloud = 0 points. Sourced from Open-Meteo for your specific location.
What Your Score Means
Poor space weather conditions — either solar wind is weak, Bz is northward, or skies are completely overcast. Not worth going outside tonight.
Marginal conditions. Some activity present but significant limiting factors (heavy cloud, moderate Bz). Worth monitoring — conditions could improve.
Good conditions. A combination of favorable solar wind and reasonable sky clarity. Consider getting outside and heading to a dark location.
Strong aurora expected. Good Bz, fast solar wind, and clear skies align for a memorable display. This is a great night to be outside.
Geomagnetic storm conditions. Bright, dynamic aurora with rapid movement. This is a once-in-a-season event — get to a dark location immediately.
Why Not Just Use the KP Index?
- ✗Global average — not location-specific
- ✗Updated every 3 hours — slow to react
- ✗Does not include cloud cover
- ✗Does not weigh Bz separately
- ✗Does not account for solar wind speed
- ✓Local cloud cover for your exact location
- ✓Updated every 2 minutes from NOAA ACE/DSCOVR
- ✓Bz separately weighted at 45% — the key factor
- ✓Solar wind speed contributes independently
- ✓Combines 5 real-time inputs into one location-aware score
When they diverge: A KP of 3 with Bz at −18 nT, 650 km/s solar wind, and clear skies may score 72% on AuroraVision — an excellent night to go out — while the KP alone would suggest only marginal activity. Conversely, KP 5 under 100% cloud cover scores near 0% because you simply cannot see the aurora.
Data Sources
See Tonight's Score
The visibility score is live now. Check tonight's Bz, solar wind, and cloud cover all in one place.