What is the Kp index and how does it relate to the Northern Lights?
Knowing when and where the Northern Lights will be visible is a challenging game and can partially be predicted by referencing the "Kp" Index, which measures the strength of geomagnetic activity, for where you are skywatching from.
Northern lights dance over Maine
Time-lapse video from Millinocket Lake, Maine showed the northern lights over Mount Katahdin, the northern terminus of the Appalachian Trail.
Have you ever seen the Northern Lights?
The popular natural phenomenon that illuminates the sky with glowing hints of vibrant color is a magnificent sight to behold, if you're lucky enough to see it. Knowing when and where the Northern Lights will be visible is a challenging game and can partially be predicted by referencing the "Kp" Index, which measures the strength of geomagnetic activity, for where you are skywatching from.
7 THINGS TO KNOW ABOUT THE NORTHERN LIGHTS
The index is determined using a network of observatory stations around the globe. NOAA's Space Weather Prediction Center calculates real-time estimates of the Kp index using 8 of the 13 network stations located in Alaska, Virginia, Canada, Germany and Australia.
Aurora Borealis displays usually follow a few days after solar events known as coronal mass ejections or solar flares. The flares bring a barrage of electrons that interact with oxygen and nitrogen in Earth's magnetic field which surrounds the outside of our planet.
Kp5 and above intensity northern lights (aurora borealis) appear in the sky over autumn trees as it lit up the sky in shades of green in Anchorage, Alaska, United States on September 29, 2025. This natural phenomenon was observed by locals, photographers and tourists.
(Hasan Akbas/Anadolu / Getty Images)
You can gauge the potential southern migration of the aurora by first finding your geomagnetic latitude, which is based on magnetic poles, not the latitude based on relation to the geographical North Pole. Geomagnetic latitude helps forecast whether a storm might be powerful enough to produce a stunning natural light display.
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Then, track the forecasted "Kp" index — a 1-9 scale measuring geomagnetic storm intensity.
According to NOAA, when the measurement is between 0-2, the aurora will be further north, dim in intensity and not active. For a 3-5 Kp index, the aurora will move further from the magnetic poles, and become brighter with more motion and formations across the sky, offering a breathtaking sight.
When the kp reaches the 6-7 range, the aurora becomes even brighter and more active, spanning further away from the poles, and offering glimpses in major cities like Seattle and Chicago.
MORE INFO: Current Kp Index | Forecasted Kp Index
The most active range in the Kp Index, from 8-9, the aurora will move closer to the equator and create the most active and stunning views directly overhead in the northern portion of the United States, showcasing the most photogenic aurora oval displays.
Northern lights or aurora borealis illuminate the night sky over a camper's tent north of San Francisco in Middletown, California on May 11, 2024. The most powerful solar storm in more than two decades struck Earth, triggering spectacular celestial light shows from Tasmania to Britain -- and threatening possible disruptions to satellites and power grids as it persists into the weekend. (Photo by JOSH EDELSON / AFP) (Photo by JOSH EDELSON/AFP via Getty Images)
(Getty Images)
Auroras are best seen in the polar regions such as Alaska, northern Canada and Scandinavia as solar activity gravitates to the polar regions.