Last night August 12, 2024 the spectacle of the Northern Lights and of the auroral arcs (SAR) unexpectedly returned to the skies of Northern Italyespecially along the Alpine arc in Veneto and Lombardy, right at the same time as the peak of the Perseid meteor shower. A double show in the sky for those lucky enough to be in the right place at the right time.
THE auroral phenomena last night’s events were due to the intensification of a geomagnetic storm that had hit the Earth yesterday morning following at least three coronal mass ejections by the Sun in recent days. Auroras and SARs were already spotted in Italy and other countries during the night between August 11th and 12th. Yesterday afternoon the storm had reached category G3 (“strong” according to the official classification), but contrary to forecasts the intensity of the geomagnetic disturbance increased instead of decreased, reaching around 5 pm yesterday (Italian time) the Category G4therefore “severe” but still smaller than the G5 geomagnetic storm (the maximum possible) that hit the Earth in May.
A G4 storm is capable of bringing Northern Lights visible even at latitudes of 45°so those of Northern Italy. And in fact there have been some sightings of auroras and SAR in the mountainous areas of the northern regions. The photos in this article were taken around 11:30 pm by the astrophotographer Andrea Vanoni to Mount Baldoon Lake Garda, between the provinces of Verona and Trento.
These photos probably show aNorthern Lights and not a SAR. The reasons are mainly two:
- the vertical “pillar” development is common in auroras but almost absent in SARs;
- Under the red aurora, the upper reaches of the underlying green aurora are clearly visible.
In fact, the green aurora, typical of high latitudes, is due to the excitation of the molecules of oxygen at relatively low altitudes (100-300 km) by high-energy charged particles from the Sun, while the red aurora is caused by the excitation of single oxygen atoms in the upper atmosphere (above 300-400 km). Since the auroras form at much higher latitudes than ours, in Italy we see the red aurora because the distance allows us to see only the highest portions. However, the fact that we can see green under the red in these photos is a clue that supports the hypothesis that we are observing a single aurora with two components, one green and one red.
Unfortunately there have not been many sightings in Italy, mainly due to security reasons. timing: the “severe” geomagnetic storm conditions that make the auroras visible in Italy arrived while it was still broad daylight in our country, so we were able to observe the auroral phenomena only many hours laterwhen the sky became dark and at the same time the intensity of the geomagnetic disturbance had diminished.
