How Wednesday’s solar eclipse could help scientists understand the universe

A solar eclipse sweeping across parts of the Northern Hemisphere on Wednesday is offering scientists and skywatchers a rare opportunity to study the sun, while also highlighting how eclipses have helped astronomers better understand the wider universe.

The Moon will pass directly between Earth and the Sun, with a total eclipse visible along a narrow path through Greenland, Iceland and northern Spain. Ireland will experience a partial eclipse.

Oisin Creaner, an assistant professor of astrophysics at Dublin City University who writes for Irish broadcaster RTE, said eclipses remain valuable scientific events.

"The more you think about eclipses, though, the more questions you have-these questions have fascinated astronomers from the time of Newgrange right up to today, when eclipses help us learn about the Sun and the fundamentals of the universe," he said.

Unlike most eclipses, those seen from Earth can produce a striking coincidence: the Sun and Moon appear almost exactly the same size in the sky. The sun is around 400 times wider than the moon but is also roughly 400 times farther from Earth.

That alignment allows the Moon to block the Sun's bright surface during a total eclipse, revealing its outer atmosphere, known as the corona.

"The close match in apparent size means that, during a total solar eclipse, we can see very close to the Sun without being blinded by its bright surface," Creaner wrote.

Eclipses have also played a role in testing fundamental physics. In 1919, observations during a total eclipse showed that the apparent positions of stars near the Sun shifted in the way predicted by Albert Einstein's theory of general relativity.

The same basic principle of a transit is now being used far beyond our solar system. When an exoplanet passes in front of its star, the resulting dip in starlight can reveal information about the planet's atmosphere and its chemical composition.

Creaner said such observations could eventually help scientists search for signs of life on worlds orbiting other stars.