Northern lights explained: aurora ovals and the Kp scale on 23 October 2026
Kp Forecast editorial team · · 3 min read
The northern lights, or aurora borealis, are light emitted when electrons from the magnetosphere hit oxygen and nitrogen in the upper atmosphere above the polar regions. The southern counterpart is the aurora australis. At 07:00 UTC on 23 October 2026 the planetary Kp index read 1.67, below G1, and NOAA SWPC put the largest Kp for the following 24 hours at 3.
What are the northern lights in plain terms?
The northern lights are the aurora borealis, light produced when electrons accelerated in the magnetosphere travel down the magnetic field lines toward the polar regions and collide with oxygen and nitrogen in the upper atmosphere. According to NOAA SWPC, the aurora typically forms 80 to 500 km above the surface, in two ovals centred on the magnetic poles. The southern version is the aurora australis.
Colour depends on the gas and the altitude. Per NASA, green from oxygen at about 100 to 200 km is the most common colour, red comes from oxygen above 200 km, blue from nitrogen at about 100 to 200 km, and pink or reddish purple at the lower edge from nitrogen below about 100 km.
Where do the northern lights form?
The ovals sit around the magnetic poles, and the best place to watch is under the oval, between about 60 and 75 degrees latitude, where NOAA notes the aurora can be seen on more than half of the nights of a year. The sky must be dark and clear, and the midnight sun blocks observation at auroral latitudes in summer.
Distance from the oval is measured in geomagnetic latitude. Per NOAA's viewing tips, the oval edge sits near 66 degrees geomagnetic latitude at Kp 0 and moves about 2 degrees closer to the equator for each Kp level. On that rule, Tromsø at 67.5 degrees geomagnetic latitude needs Kp 1, Edinburgh at 58.1 needs Kp 4, and Kiel at 54.4 needs Kp 6. The locations page lists the figure for each destination.
Why do the northern lights move south during a storm?
A geomagnetic storm expands the ovals toward the equator. The NOAA G scale describes how far the aurora is seen: G1 at Kp 5 as low as northern Michigan and Maine, G2 at Kp 6 as far as New York and Idaho, G3 at Kp 7 to Illinois and Oregon, G4 at Kp 8 to Alabama and northern California, and G5 at Kp 9 to Florida and southern Texas.
The Kp index itself runs from 0 to 9 in 3-hour slots, as published by NOAA SWPC. At 07:00 UTC on 23 October 2026 the reading was Kp 1.67, measured at 03:00 UTC, with the NOAA scale below G1 and no active alert. Solar wind stood at 411.2 km/s, density 3.88 p/cm3 and Bz 0.45 nT. NOAA put the largest Kp for the next 24 hours at 3, which is a forecast figure, not a measurement. The live forecast page tracks these numbers as they update.
What are the northern lights not?
They are not a nightly guarantee at any single spot. NOAA's 3-day forecast gives Kp in 3-hour slots and the 27-day outlook gives only a daily largest Kp, which is a daily maximum and never a forecast for a particular night. Kp Forecast is an independent site that shows NOAA SWPC data, not an official space weather service.
Frequently asked questions
What are the northern lights and where do they come from?
The northern lights are the aurora borealis, light from oxygen and nitrogen in the upper atmosphere after electrons from the magnetosphere collide with them above the polar regions, per NOAA SWPC. The aurora typically forms 80 to 500 km above the surface.
Do the northern lights move south when Kp rises?
Yes. A geomagnetic storm expands the auroral oval toward the equator, and the NOAA G scale maps this: G1 at Kp 5 can be seen as low as northern Michigan and Maine, and G5 at Kp 9 as far as Florida and southern Texas.
What Kp do the northern lights need in Tromsø?
Kp 1. Tromsø sits at 67.5 degrees geomagnetic latitude, and on NOAA's oval rule the edge reaches that latitude at Kp 1, so the city is under the oval at almost any activity level.
Were the northern lights visible on 23 October 2026?
At 07:00 UTC on 23 October 2026 the Kp reading was 1.67, below G1, with no active NOAA alert. NOAA put the largest Kp for the next 24 hours at 3, a forecast figure rather than a measurement.
Text written with AI from NOAA SWPC data and automatically checked against editorial rules before publication. Figures come from the linked sources. Kp Forecast is not an official space weather service.