From Solar corona to human emotions: What can we learn from eclipses? (2/4)

Eclipses tell the story of humanity’s relationship with knowledge. Once seen as dire omens, they have become open-air laboratories, feared for centuries and now closely studied by scientists in a continuity stretching back to the earliest observations of Antiquity.

One of the earliest traces of an eclipse observation may be a clay tablet discovered in the city of Ugarit, in present-day Syria, dating back to 1223 BCE.

In ancient civilisations, the sight of the sun vanishing in broad daylight inspired both wonder and dread.

 

In ancient China, the phenomenon was seen as a sign that a dragon was devouring the Sun because of humanity’s misconduct on Earth. Drums were beaten to frighten the beast away and bring back daylight.

In South America, the Incas interpreted eclipses as a sign of the sun god’s anger. Their leaders would try to guess the cause and appease it with a sacrifice.

A solar eclipse over the Greek island of Paros in 648 BCE inspired the following words from the poet Archilochus: “Nothing in the world can surprise me any longer. For Zeus, father of the Olympians, has plunged midday into black night by blotting out the light of the rising sun, and a dark terror now hangs over men. Anything can happen.”

Beyond myth, eclipses also helped advance knowledge from very early on. As far back as Antiquity, observing them helped people better understand the movements of celestial bodies and predict their return.

This scientific role only grew stronger over the centuries, eventually enabling some of the most significant discoveries in modern astronomy.

That was the case in 1868, when helium – named after the Greek “helios”, meaning Sun – was discovered in the Sun’s spectrum before it was even identified on Earth.

The solar eclipse of May 29, 1919, visible from central Brazil to East Africa, also left its mark on science, having made it possible to prove Einstein’s theory of general relativity through measurements of the deflection of starlight by the Sun.

Understanding of the solar corona – itself identified in 1842 as part of the Sun, not the Moon as had previously been believed – the solar wind and the phenomena behind space weather has improved accordingly.

At a time when satellites monitor the Sun continuously, eclipses might seem to have been relegated to the status of curiosities. Yet they remain valuable natural laboratories, still allowing scientists to make observations impossible to obtain otherwise, in both life sciences and humanities.

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Understanding the Sun’s structure

Instruments now exist – coronagraphs – that create artificial eclipses by blotting out the central portion of the star as seen through a telescope. But they remain less effective than the Moon at masking the solar disk.

“An eclipse is a natural way of masking the Sun, which is extremely bright,” said astrophysicist Antoine Strugarek, who added that the Sun’s brightness makes it difficult to observe its edges and structure.

“It’s a bit like trying to watch a fly buzzing next to a car headlight,” he told FRANCE 24.

Studying the structure surrounding the Sun is therefore essential.

“Everything that happens in Earth’s magnetosphere, in the ionosphere, and that affects conditions for our satellites, our astronauts, our flight crews aboard aircraft … all of that comes from the Sun,” Strugarek said.

To understand these phenomena, scientists need data. But powerful enough observation and measurement instruments still need to be placed along the eclipse’s path of totality. Observation campaigns bringing together professional and amateur astronomers are organised to gather as many images as possible.

Astronomers will position themselves all along the band of totality in Spain on August 12 to capture a large number of images of the eclipse, Strugarek said.

On the other side of the Pyrenees, where the eclipse will only be partial, French scientists will simply check whether their models work properly in predicting the evolution of the solar system.

A single eclipse is not enough to fully understand the underlying physical mechanism, but it can help answer major questions the scientific community is grappling with, including a mystery that has intrigued for decades: the temperature of the solar corona, which reaches 1.5 million Kelvin, or more in certain places, while the Sun’s surface itself is “only” 5,800 Kelvin.

Such discoveries would allow scientists to extrapolate their knowledge of the Sun to other stars, and thereby better understand exoplanetary systems.

Animal behaviour under watch

Astronomers and astrophysicists are not the only ones interested: biologists are also drawn to these rare celestial events.

A team of Spanish researchers has put out a call to recruit 300 volunteers for the fateful day to analyse how animal species react to a sudden onset of darkness in the middle of the day.

The experiment, named EcoEclipse, involves installing a sound recorder two days before the eclipse and removing it two days after, in order to compare animals‘ vocal responses and the behaviour of certain species before, during and after the phenomenon, with birds and bats being the main focus.

“Trying to better understand how animals react will help us better understand their vulnerability and sensitivity to changes in light, which matters in the context of light pollution,” said Irene Mendoza, an ecologist at the University of Seville who specialises in ecoacoustics.

Bat behaviour will be watched particularly closely. Experts suspect their habits will be disrupted when they mistake the eclipse’s twilight for nighttime darkness. Because this eclipse will occur in the early evening, the main hypothesis is that bat activity will pick up much earlier than usual.

Earlier work during eclipses has already shown various reactions among animals. “Bees rush back into their hive very quickly and in large numbers, primates gather together while signalling towards the sky, daytime birds fall silent, while nocturnal ones become active,” Mendoza said.

Other species, including elephants, lions, primates and bears, will also be observed as part of an initiative coordinated by the Iberian Association of Zoos and Aquariums (IAZA), which will record in real time behavioural changes in a wide variety of diurnal and nocturnal animals during the eclipse.

A dozen Spanish zoos, strategically located along the eclipse’s path, will take part.

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Effects on the human body and mind

The phenomenon also produces effects on humans that science has only recently begun to examine, although the body of research remains limited.

During the 2017 eclipse in the United States, researchers at the University of California studied nearly three million social media posts from people located both inside and outside the path of totality, a band stretching from Oregon to South Carolina.

The study’s results, published in 2022, found that those who witnessed totality expressed more intense feelings of awe and used language that was less self-centered and more prosocial, supportive, humble and collective.

A pilot feasibility study also attempted to measure the brain and heart responses of observers during an annular eclipse – when the Moon’s apparent size is slightly smaller than the Sun’s – in New Mexico in 2023.

British psychologist Kate Russo and researcher Andrew W Bailey, who led the study, reported brainwave variations consistent with episodes of awe at the moment of the eclipse, though the results remain exploratory.

The American Astronomical Society described the work as the first attempt to use biometric technology to study the emotion of awe during an eclipse.

A similar experiment will be carried out again during the total eclipse on August 12 by Catalan scientists, who have launched a large-scale citizen science project to study how a total solar eclipse affects the human body.

The initiative, called “Project Solaris” and led by the Catalan government, will collect biometric data from the smartwatches of 5,000 volunteers before, during and after the total solar eclipse.

“We are facing a unique opportunity to bring science closer to society,” astrophysicist Eduard Masana said.

The data collected will be studied by researchers at the Vall d’Hebron Research Institute (VHIR) in Barcelona to find out what happens when thousands of people experience the eclipse at the same time, and how the emotions triggered by the event affect their heart rate and breathing.

“It’s a very unusual situation. Suddenly, it’s dark, the temperature drops, and thousands of people experience this unique moment together,” said Maria Jesus Cruz Carmona, head of the pulmonology research group at VHIR. “We believe all these factors have a physiological impact, and that’s precisely what we want to study.”

Despite centuries of observation, a few minutes of eclipse are still enough to open up new avenues of research.

This article was translated from the original in French.