Finding your location…
Checking the sky
- Kp
- –
- Hp30
- –
- Solar wind Bz
- –
- Wind speed
- –
- Peak Kp, 24h
- –
- Cloud
- –
What do these numbers mean?
- Kp
- The standard 0 to 9 measure of how disturbed Earth’s magnetic field is, updated every three hours. Around 5 or more is a geomagnetic storm, and the higher it goes the further south aurora can be seen.
- Hp30
- Kp’s finer cousin from GFZ Potsdam: the same idea measured every 30 minutes, so it reacts faster, and it can go above 9 in extreme storms.
- Solar wind Bz
- The north-south direction of the magnetic field carried in the solar wind. When it points south (negative, ideally below −5 nT) it connects with Earth’s field and feeds the aurora. Positive values tend to shut things down.
- Wind speed
- How fast the solar wind is passing the satellite, in km/s. Around 400 is calm; 600 or more drives stronger displays.
- Peak Kp, 24h
- The highest Kp over the last day, a quick way to see whether tonight is quiet or a storm has just passed.
- Cloud
- Forecast cloud cover over your spot right now. Under about 30% is good for looking; over 80% hides the sky.
Solar wind readings come from a satellite about 1.5 million km sunward, so they lead what reaches Earth by roughly 30 to 60 minutes.
What decides tonight
A sighting needs three things at once: solar activity strong enough to push the aurora down to your latitude, a properly dark sky, and gaps in the cloud. Whichever is weakest sets your chances.
Kp needed here
Next 24 hours
UnlikelyPossibleGoodStrong
Taller and brighter means a better chance. Glowing bars are the best window. Tap a bar for the hour’s score and cloud. Assumes current solar activity holds.
UK and Ireland cloud cover
Where it is clear enough to look right now. Open-Meteo.
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Bristol: what Kp do you need?
- Kp 2+Faint glow, camera only
- Kp 4+Low on the northern horizon
- Kp 6+Well up in the northern sky
- Kp 7+Overhead or high in the sky
Estimates from a simple model, assuming a clear dark sky. They are rough guides, not guarantees.
When to look
- SeasonSeptember to March, when nights are long enough.
- HoursRoughly 10pm to 2am local time, around magnetic midnight.
- SkyAim for under 30% cloud, and avoid a bright moon if you can.
- WhereFace north with an open horizon, away from street lights.
Nearby: Newcastle · Carlisle · York · Manchester · Birmingham · Norwich
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