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Our ability to see the aurora borealis, aka the northern lights, in Sandpoint depends mainly on two factors, geomagnetic activity (the degree of disturbance of the earth's magnetic field at the time, which itself is triggered by solar storms; when activity is high the aurora is bright) and our geomagnetic latitude. And of course other considerations are cloud cover at the time of the activity, whether there is a full moon and so forth.
Sandpoint is located at about 54 degrees magnetic latitude. When geomagnetic activity is low, the aurora typically is located, in the hours around midnight, at about 67 degrees magnetic latitude – in other words, far north. As activity increases, the region of the aurora expands southward toward the equator. At our latitude when geomagnetic activity is moderately high we can get excellent displays, normally several times a year and subject to the cloud cover.
Auroras are also seasonal – more active and visible in fall and spring than in summer or winter. This seems surprising, since the aurora is trigged by solar activity, and the sun doesn’t know what seasons are occurring on Earth. Scientists postulate that the seasonality is due to the tilt of the sun and Earth’s respective magnetic fields, causing them to link up during fall and spring, plus a bit of wobble in the Earth’s rotation.
For skywatchers in Sandpoint, the northern lights can create fantastic displays. And nowadays, thanks to satellite measurements of the solar storms and geomagnetic activity that kick off the northern lights, it is possible to obtain forecasts. There is a simple index called Kp, a number from 0 to 9, which is used to refer to geomagnetic activity for a 3-hour period. At our magnetic latitude we need a Kp of 5 to 7 for a good display of the northern lights. The Space Weather Prediction Center provides a variety of tools and information including near-real time predictions of Kp numbers and an aurora forecast.
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