Northern lights could return to Portugal tonight: how are they formed? | Astronomy

In a phenomenon considered rare and which had not been seen in Portugal for many decades, the country was able to witness the Northern Lights on the night of Friday to Saturday, in several locations. Here we explain what is happening to the Sun, how the auroras appear and what experts expect in the coming days.

What happens on the Sun to make us see auroras in unusual places, like Portugal?

The solar cycle – which is 22 years long on average – is reaching its maximum in this year 2024, so we are seeing great activity on the Sun. This peak of activity, about every 11 years of the 22-year cycle , translates into more active sunspots and the ejection of more material by the Sun into space. Over the past few weeks, there have been several class X solar eruptions – the largest and most energetic in the classification of solar eruptions known as “coronal mass ejections”, or CME for short.

These coronal mass ejections are eruptions of ionized gases at high temperatures from the solar corona, the outermost layer of the Sun’s atmosphere. When these gases, which are part of the solar winds, reach the Earth’s magnetic field, they can disturb it. In other words, they can give rise to geomagnetic storms and, of course, an unforgettable spectacle of auroras in the skies of Earth. The materials coming from the Sun interact with the gases and particles present in the Earth’s atmosphere and the luminous effects of the aurora borealis are produced.

Geomagnetic storms are also classified according to the disturbance they cause in the Earth’s magnetic field: called “G index”, they range from a scale of 1 to 5. A G5 storm is therefore considered “extreme”.

Well, last week there was strong solar activity, as said by two researchers from the Department of Physics at the University of Coimbra, Fernando Pinheiro and Alexandra Pais, who sent information to PÚBLICO about what is happening on the Sun. “ There have been several class X solar flares, originating in the active region of the Sun ‘called AR3664’, a cluster of sunspots 16 times the diameter of Earth. From this region there were five ejections of coronal matter between the 8th and 9th of May, which headed towards Earth”, explain the two researchers.

“The arrival of the first CMEs in the vicinity of Earth took place at around 6pm on Friday, May 10th, being felt in the sudden increase in the intensity of the magnetic field observed, for example, at the Coimbra magnetic observatory”, continue the scientists. “This increase in intensity is caused by the compression of the Earth’s magnetosphere, on the side facing the Sun, as a result of the CME collision. This interaction resulted in a strong disturbance of the Earth’s magnetic field – [ou seja,] a geomagnetic storm – classified by the North American agency NOAA with the G5 index, on a scale of 1 to 5.”

In short, according to classifications by NOAA, the North American agency for the ocean and atmosphere, the Sun has recorded several class X solar flares in recent days, which have caused a G5 geomagnetic storm.

Is there a less pretty side to geomagnetic storms?

Yes. If the beautiful side of geomagnetic storms is the one that allows us to observe auroras, the less positive side is precisely the disruption they can cause in systems crucial to today’s civilization.

“This is the type of event that can cause various disturbances in the services provided by satellites, such as communications and global positioning, in communication services via high frequency radio waves, in addition to disturbances in the transport infrastructures of electrical energy and in automatic train cornering systems that control the occupancy of the lines”, explain, in the statement sent, Fernando Pinheiro and Alexandra Pais.

The two researchers also recall that the last G5 geomagnetic storm occurred more than 20 years ago, in October 2003: “It caused power cuts in Sweden and damaged transformers in South Africa.” And they specify: “The storm we are witnessing is exceptional. It is more intense than the one in October 2003, which caused blackouts in Sweden and South Africa, but it is not as intense as the one in March 1989, which caused a major nine-hour blackout in Canada”, they contextualize.

“These effects occur simultaneously with the colorful aurora borealis (in the North) and southern lights (in the South). As a rule, they are more intense at latitudes closer to the poles. Countries such as Sweden and Canada (in the Northern Hemisphere) or New Zealand and Australia (in the Southern Hemisphere) have a long history of recording this type of incident and the occurrence of spectacular auroras”, say the Coimbra researchers about the positive aspects. and less positives from solar flares and geomagnetic storms. “But the night from Friday to Saturday, May 11th, was special, because it also offered us, in Portugal, auroras in various parts of the country.”

In which areas of Portugal have the Northern Lights been seen?

Countless reports have been flooding social media since this Friday with the sharing of photographs taken from various places in Portugal – from the northernmost regions of the mainland, such as Moimenta da Beira, Viseu, Coimbra or Guarda, to Alentejo, such as Portalegre –, including the Azores and Madeira.

Contrary to scientists’ initial expectations for the year 2024, the northern lights have arrived in Portugal. I knew that the Sun would reach maximum activity in the solar cycle this year and that this could bring more intense northern lights in low latitude locations around the planet, but several experts interviewed by PÚBLICO at the beginning of the year curbed expectations, a as this phenomenon is very rare to be visible in Portugal. That’s why they considered it unlikely that we would be lucky enough to observe the Northern Lights in Portugal in 2024, given the country’s distance from the North Pole.

After all, the Northern Lights arrived here on the night of May 10th to 11th. The sky was filled with pink tones. And there is hope that they will return tonight from Saturday to Sunday and even the following ones. Since the maximum of the current solar cycle is yet to arrive, Fernando Pinheiro and Alexandra Pais now consider that perhaps other “more intense” geomagnetic storms are on the horizon: “Let’s pay attention to the magnetometers, and take a look at the sky over the next few nights!”

In addition to Portugal, the auroras from the 10th to the 11th of May went around the globe, in lower latitudes, marveling everywhere, from Canada and much of the United States (going as far as California or Alabama ) to France, the United Kingdom, Switzerland, Germany, the Netherlands, the Canary Islands, Hungary, Ukraine or Russia. In the Southern Hemisphere, there are records of auroras in the skies over New Zealand and the Antarctic Peninsula, for example.

Where is the best place to see the auroras?

The best place to enjoy such a show of colorful lights in the sky is always closer to the Earth’s poles, both the North Pole (for the Northern Lights) and the South Pole (for the Southern Lights). Therefore, in Northern European countries, such as Sweden and Norway, it is more common to see aurora borealis than in Southern countries. The phenomenon takes on a variety of bluish or greenish colors there.

Outside of these places, and having now arrived in Portugal, the recommendation for seeing the northern lights in all their splendor, if they occur again, is to look for places with low light. This is so that they are not dazzled by the lights of cities and towns.

It is precisely to a very dark place that, by coincidence, an initiative that promoted a telescope gathering this weekend, in the municipality of Moimenta da Beira, will move from Saturday night to Sunday. The 8th Telescope Concentration in Moimenta da Beira, between the 10th and 12th of May, brought together more than 120 telescopes and 200 people, including amateur and professional astronomers from Portugal and Spain, for lectures, sky observations, sharing of knowledge and socializing .

“On the first night of observations we were treated to these auroras. The astronomers who were photographing the sky noticed the appearance of the aurora borealis, which is not normal in the latitudes where we found ourselves, and it was delirium”, tells us Paulo Sanches, professor of physical chemistry, who is the founder and the coordinator of the Science Club of the Moimenta da Beira School Group. “Everyone taking photos, everyone sharing photos. It was fantastic, because we weren’t expecting this.”

The participants of the 8th Telescope Concentration in Moimenta da Beira even met at the municipal stadium, in the middle of the town, which had turned off the public lighting on purpose for the initiative. And, by coincidence, the auroras appeared. On the night of this Saturday to Sunday, more than 120 telescopes will peer at the sky at the Sanctuary of São Torcato, 12 kilometers from the town of Moimenta da Beira. “The sky there is darker. According to experts, sun watchers, we may still be able to see auroras tonight, perhaps not with yesterday’s spectacle, but there is a high chance of seeing them tonight, because solar storms take some time.”

Since 2009, Paulo Sanches has organized the Telescope Concentration in Moimenta da Beira. “In 2009, the International Year of Light was celebrated and I remembered: if there are gatherings of motorbikes, why not have a gathering of telescopes? It was a huge success in the first year, which we repeated every two years”, says Paulo Sanches.

Have there been other northern lights observed in Portugal worth noting?

Yes, and some northern lights were even featured in the newspapers at the time. For example, on February 4, 1872, a super solar storm shook the Earth and caused the aurora borealis to cover the Earth. There were reports in newspapers not only in India, Spain, France and Wales, but also in Portugal. It was seen in Guimarães, Coimbra, Porto, Aveiro, Setúbal and Lisbon, as concluded by José Ribeiro and Ana Correia, physics and chemistry teachers at the Secondary School with 3rd cycle of Henrique Medina (in Esposende), who were involved in an international study on this superstorm published, at the end of last year, in the magazine The Astrophysical Journal.

O Porto newspaper published the following report two days after the dawn of February 4, 1872: “Aurora borealis. This meteorological phenomenon reappeared yesterday evening, extending from east to west and heading north. It began to distinguish itself perfectly in the atmosphere, despite being covered in clouds, there at around seven o’clock at night, being visible over a wide space. The night was unfavorable for observing this phenomenon, so common in the polar regions.”

About ten years ago, José Ribeiro and Ana Correia carried out a survey of the northern lights seen in Portugal in the 19th and 20th centuries. In this teaching material, entitled Northern Lights Observed in Portugal, there are curious records of this phenomenon in the country over the last 200 years. For example, on January 21, 1957, the Lisbon Diary there was an aurora borealis seen in various parts of the country. Or, before that, on January 25, 1938, the newspaper The Cávado reported the sighting of this phenomenon in Esposende.