About AuroraCast

What this is

The aurora — the northern lights (aurora borealis) and their southern twin (aurora australis) — is light given off when charged particles from the Sun, funneled by Earth’s magnetic field, slam into gases high in the atmosphere. Most of the glow happens between about 100 and 300 km up, where oxygen lights up green (around 557 nm) and red, and nitrogen adds blue and purple fringes.

AuroraCast turns NOAA SWPC space-weather data into a plain answer to one question: how likely are the lights tonight, and how far south might they reach? The key number is the Kp index — a 0–9 scale of global geomagnetic activity. The higher the Kp, the lower the latitude where the aurora becomes visible, so a quiet Kp 2 stays near the poles while a storm-level Kp 7 can bring the lights to mid-latitudes.

• 🌌 How auroras formFrom solar wind to glowing sky — how charged particles, Earth’s magnetic field and atmospheric gases combine to paint the aurora’s colors.
• 📈 The Kp index and geomagnetic stormsWhat the 0–9 Kp scale measures, how higher Kp pushes the aurora toward the equator, and how Kp 5+ maps to NOAA’s G1–G5 storm scale.
• ☀️ The Sun’s role: solar wind, flares and the solar cycleWhere the energy comes from — sunspots, solar flares, coronal mass ejections, the solar wind and the roughly 11-year cycle that drives aurora seasons.
• 🔭 How and when to see the auroraTurning a forecast into a sighting — dark skies, the right direction, the best hours and seasons, and how much warning the forecast gives you.

Aurora-viewing guidance by Kp and conditions

Practical guidance for turning a forecast into a sighting. Kp sets the odds and how far south the lights may reach; clear, dark skies and timing do the rest. Treat forecasts as probabilities, not promises.

Data sources

• NOAA SWPC — The US Space Weather Prediction Center — the planetary Kp index, G-scale storm alerts and the OVATION aurora forecast.
• NOAA SWPC Aurora Forecast (OVATION) — Near-real-time maps of the auroral oval’s location and intensity, plus the 30-minute aurora outlook.
• GFZ Potsdam Kp index — The German Research Centre for Geosciences derives the definitive planetary Kp index (three-hourly, back to 1932). AuroraCast carries the last 90 days of it alongside the live NOAA feed. Licensed CC BY 4.0.
• DSCOVR & ACE solar-wind monitors — Spacecraft at the L1 point sampling the incoming solar wind, the basis for short-term (~30–90 min) aurora lead time.

Frequently asked

What Kp do I need to see the aurora?

It depends on your latitude. Near the auroral zone, Kp 2–3 can be enough; mid-latitudes generally need a storm — Kp 5 and up (G1+) — for a realistic chance. Higher Kp pushes the lights further from the poles, so check the viewing line for your location.

How much warning does the forecast give?

Two scales. Days ahead, an Earth-directed CME flags a likely storm one to three days out. Minutes ahead, solar-wind monitors at the L1 point (DSCOVR and ACE) typically give about 30 to 90 minutes of lead once a gust is detected — enough time to get outside.

When is the best time of year and night?

Aim for the dark half of the year — autumn through early spring at high latitudes, since summer nights never fully darken. Activity tends to peak around local midnight, and the weeks around the March and September equinoxes are statistically a bit more storm-prone.

Why does my photo show colors I couldn’t see?

Your eyes struggle with faint color in the dark, so a modest aurora can look pale gray-green by eye. A camera’s longer exposure gathers more light and reveals the pinks, reds and greens — which is why a tripod shot often confirms a glow your eyes weren’t sure about.

Does a high Kp guarantee I’ll see the lights?

No. Kp is a planet-wide, three-hour average that tells you the odds, not a local guarantee. You still need a clear, dark sky, a view toward the pole, a low Moon and good timing. Clouds or city light can hide even a strong display.