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    Kp index explained

    What the number means, how much Kp you need this far north, and why cloud cover matters more.

    What is the Kp index?

    The Kp index is a number from 0 to 9 that describes how disturbed the Earth's magnetic field is. It is worked out from magnetometers at stations in several parts of the world and given for three hours at a time. The official index comes from GFZ in Potsdam, and NOAA in the United States publishes a Kp forecast for the coming days.

    A high Kp means a wider, stronger auroral oval. A low Kp does not mean an empty sky. That depends on where you are standing.

    The Kp scale, step by step

    How we read the numbers here at 69 degrees north.

    Quiet

    Kp 0–1. Little activity. A faint arc can still show on a dark, clear evening.

    An ordinary night

    Kp 2–3. Often enough for clear arcs and bands above us when the sky is clear.

    Active

    Kp 4. More movement and colour, and the lights tend to cover more of the sky.

    Storm

    Kp 5–9. A geomagnetic storm. The aurora is seen far to the south, and here it may be right overhead.

    How much Kp do you need near Senja and Tromsø?

    Many visitors think they have to wait for Kp 5. That is true further south. We are at 69 degrees north, inside the auroral zone, where the northern lights are often visible at Kp 1 to 3. The same goes for Senja and Tromsø.

    Three things have to be in place, and Kp is the least important of them.

    Darkness. The season runs roughly from September to late March. In summer it is too light.

    A clear sky. The aurora is far above the clouds. Under thick cloud you see nothing, whatever the Kp.

    Activity. Kp 2 under a clear sky beats Kp 6 behind cloud.

    Northern lights tonight? How to read the aurora forecast

    There are three numbers to look at. Our live aurora forecast is made for Dyrøy, near Senja, and shows them together.

    Cloud cover as a percentage. Start here: the lower, the better.

    Kp index right now, with an activity level.

    Probability of aurora, and the best time of the evening.

    Kp is the same in Tromsø as it is near Senja. Cloud cover is local, so check it for where you are.

    A forecast is a guide, not a timetable. Kp is one figure for the whole planet over three hours, and the lights can flare up for a short while even when the number is low. If it is clear, look outside regularly from early evening until after midnight.

    Watch the sky from bed

    The easiest way to catch a short burst of aurora is to be somewhere dark with the sky above you. In one of our AuroraHuts you lie under a glass roof and can keep watch without standing outside in the cold.

    From the hotel rooms it is only a few steps out onto the veranda. The jacuzzi and the wood-fired hot tub can be booked for the evening.

    FAQ

    Questions about the Kp index and the northern lights

    A number from 0 to 9 that describes how disturbed the Earth's magnetic field is. The higher the number, the further south the northern lights can be seen.

    Near Senja and Tromsø the aurora is often visible at Kp 1 to 3, as long as it is dark and clear. A higher Kp tends to give stronger lights but is not required.

    Check cloud cover first, then Kp and probability. All three are in our live forecast at attmehave.no/en/prognose.

    When the nights are dark, roughly from September to late March or early April. From around 20 May to 23 July we have the midnight sun here, and it is too light.

    Yes. We are at 69 degrees north, by the sea in Dyrøy, with little light pollution and an open view across the water towards Senja. Even so, the aurora can never be guaranteed.

    Wait for the aurora where it is dark

    Stay a few nights and one cloudy evening matters less. Choose a glass igloo or a hotel room on the booking page.