“The storm has passed…” Leopardi would have written, with the small variant that it was a geomagnetic storm.
A few days before the astronomical event which certainly had great media coverage, Let’s return with this article to talk about geomagnetic storms category up to G5, which between 10 and 12 May were produced by a series of coronal mass emissions (CME) from the Sun.
The cause of the wonderful auroras observed in numerous areas of northern Italy
In particularwe want to focus on it on the exceptional extension of these storms and the resulting auroras to the more southern latitudes.
Repetita iuvant…a little refresher
The solar plasma (consisting of electrically charged particles) with a built-in magnetic field emitted in several consecutive episodes by the Sun at supersonic speeds within a few dozen hours it reached the Earth’s magnetic field.
The Earth’s magnetic field has a dipolar structure, made up of lines that exit from one pole and immerse themselves in the other pole, which facilitates the capture of electrical particles coming from the Sun, ferrying them towards the poles.
Solar charged particles “they excite” the ions of the Earth’s ionosphere (a process in which the electrons of the ions, receiving energy, move to higher energy levels). The same ions, later “de-energizing” (a process in which the electrons of ions from higher energy levels return to their starting levels) they emit electromagnetic radiation, that is, the particular luminescence that actually constitutes the auroras.
The video was shot by the SOHO satellite which first detected the CMEs which would have triggered the G5 category geomagnetic storm hours later.
The dipolar geometry of the Earth’s magnetic field which makes the auroras visible at high latitudes, both boreal (northern hemisphere) and southern (southern hemisphere).
Solar storms can disturb the signals of migratory birds
However, in the presence of particularly intense geomagnetic storms, precisely those of category G5 which occurred in recent days, Solar electric particles can reach even the southernmost layers of the Earth’s ionosphere.
Historical auroras in Sicily
The visibility of the auroras from Sicily was one of the events that gave ordinary people an idea of the exceptional intensity of the phenomenon.
In the memory of living Sicilians there are no precedents.
Neverthelessdespite its exceptionality and rarity, This is not a one-off event. We have to go back in time almost one hundred and fifty years. Exactly on the nights of 24 and 25 October 1870, the Northern Lights were visible from the heart of Sicily, similar or perhaps more intense than the last ones observed between 10 and 12 May.
The testimony of this event which occurred in 1870 is twofold; in fact, in addition to having multiple written testimonies, there is one designed.
A strong solar storm has caused aurora borealis even in rare places
In an interesting article from 2018 (so years before this 2024 event), written by Dr. Giada Genuarestorer of book-archival material, and at the time working at the Astronomical Observatory of Palermo, three watercolors depicting the Northern Lights are mentioned. These three watercolors were part of a series of six drawings made by Mr. Montemagno of Caltagirone and sent to the Palermo Observatory.
In them (see cover photo) some phases of the Northern Lights observed from Caltagirone are represented (at latitude 37.23 degrees north) on the nights of 24 and 25 October 1870.
Gaetano Cacciatore himself, then director of the Astronomical Observatory of Palermo, witnessed the event.
Continuing from Dr. Genua’s article, we report an extract from the “Meteorological Bulletin of the Royal Observatory of Palermo” (n.10 – Vol-VI, October 1870).
“A large mass of reddish igneous light in an almost globular shape appeared above and detached from Monte Pellegrino, which rises just in the direction of the Pole. (…) The intensity was maximum around 7.19 am and the sky then seemed like a sea of fire with continuously stirring flames. Then enormous heights of columns of a yellowish white light, continuously varying in position and shape, were seen rising from one side and the other, and often from the middle, sometimes turning into beams of large dimensions, now into luminous and lively jets. (…) The remarkable appearances presented by this phenomenon, very rare to manifest itself in our regions, made it clear to us from then on that the aurora, of which we were observers, must have been among the brightest and most splendid that had been views and news subsequently received from overseas have only confirmed our conjectures” (from the Meteorological Bulletin of the Royal Observatory of Palermo, n.10 – Vol-VI, October 1870).
That these were indeed auroras is supported by astronomical observational data relating to solar cycles.
Indeed, in 1870 the maximum activity of solar cycle number 11 was underway (we are now at the maximum of solar cycle number 25).
The numbering of solar cycles (based on the number of spots) dates back to the mid-18th century. Solar cycle number 1 began around 1755. The current solar cycle – the 25th – began in late 2019/early 2020.
Therefore, it is highly probable that CMEs occurred at that time (October 1870). similar to those that occurred between 10 and 12 May with the consequent triggering of geomagnetic storms.
The Sun will reach its solar maximum in 2024: what it means and how it may affect Earth
The maximum of the current solar cycle could last for several more months. Therefore, no wonder if we soon find ourselves admiring and writing about new auroras at Sicilian latitudes.
