Learn the aurora in 5 minutes

Short, jargon-free explainers — all nine are live. Each one takes about five minutes, ends with quick answers, and shows you exactly where its concept shows up on the live city forecasts. If you only read two, start with the Kp index (the headline number behind every verdict) and the Bz explainer (the real-time trigger the apps don't show you).

The numbers that matter

• What is the Kp index? — the 0–9 activity scale, what each level looks like from the ground, and the two traps that make people distrust it.
• Solar wind Bz, south is good — the real-time trigger behind aurora bursts, and how it gives you a 30-minute head start.

The models and the sky

• The OVATION oval model, simply — what NOAA's aurora map claims, what it can't see, and how to read it in 30 seconds.
• Why cloud forecasts fail — resolution, coastal microclimates, and the four tactics that recover most of the loss.
• Astronomical, nautical, civil twilight — why the −18° line matters more than sunset, and the midnight-sun exception.
• Moon phase vs aurora visibility — when moonlight actually matters, and the moonrise detail most guides skip.
• The Bortle scale in 7 stops — from wilderness to inner-city glare, and how far to drive.

The big picture

• Solar cycles 24 → 25 → 26 — why the current years are the best aurora odds of the decade, and what happens next.
• Field glossary — every term you'll meet on a space-weather feed, in one or two sentences each.

How the five factors become one score

Every city page combines what these guides explain separately. Geomagnetic activity sets the ceiling — no Kp, no show, whatever the sky does. Cloud cover is the most common killer: a storm overhead is invisible from underneath, which is why the cloud guide matters more than the Kp guide for most travellers. Moonlight and twilight set the contrast, and the Bortle class of your exact viewing spot decides how faint a display you can still see. The site weights these five inputs into a single 0–10 score and a one-word verdict; the full formula is published on the methodology page.

A practical rule of thumb from these nine guides: check Kp first to know if it is possible, check cloud and moon to know if you will see it, and use Bortle to decide how far to drive. That is the same order the live forecast evaluates them.

Prefer to see it applied? Every concept here is live-scored for 55 cities right now — or plan ahead with the 27-day outlook.