How a total solar eclipse in 1919 left physicists ‘more or less agog’

The following is an excerpt from the monthly Launchpad newsletter, where resident space expert Leah Crane travels through the solar system and beyond. You can sign up for Launchpad for free here.

It was in 1919 that the moon did something completely natural and blocked our view of the sun, forever changing our understanding of the universe. Observing from the African island of Principe, astronomer Arthur Eddington observed the positions of stars and planets that became visible in the eerie darkness of the day. With most of the sun’s light dimmed, he was able to see how light from distant stars is distorted when it is deflected by the sun’s gravity, an effect called gravitational lensing.

He confirmed his sightings with those of another expedition in Brazil, and these observations provided some of the first evidence for Albert Einstein’s relatively new theory of general relativity. This explanation of how massive objects distort the fabric of space-time is now considered fundamental, but at the time it was a revelation. It changed all the way we think about gravity and the universe.

It also led to my results Favorite newspaper headline So far, it has been published of new york times Later that year, “All the light in the heavens is slanted.” Scientists are more or less puzzled over the observations of solar eclipses. Triumph of Einstein’s theory The stars were determined by where they were visible and by calculation It’s not where it was, but no one needs to worry.”

“No one needs to worry” may seem like a bit of a stretch, but watching a total solar eclipse can certainly make you nervous in ways you can’t explain. I watched it for the first time in 2017. It was truly unforgettable. You might think of a solar eclipse as being like a cloudy day when clouds drift in front of the sun. After all, what’s happening is simply the moon passing in front of the sun and casting a shadow on Earth. But it’s surprisingly different.

The first thing you notice during a total solar eclipse is the moon’s shadow hurtling toward you across the ground at speeds of over 1,500 miles per hour. The extent of the shadow for April’s eclipse will be approximately 185 kilometers, but this can vary slightly based on the exact orientation of the Sun and Moon. As the shadow approaches, it looks like the moon has bitten the sun, and its light has a mysterious, foggy quality.

Suddenly, the area becomes dark. This is wholeness. Temperatures can drop up to 10 degrees. The only light comes from the sun’s outermost layer, called the corona, and ripples beyond the moon’s silhouette. It was getting dark and some stars were visible in the sky. Many animals, including birds and insects, naturally seem to think it is night, and the otherworldly twilight becomes silent, except for the chirps of awakened nocturnal insects. I don’t know how you feel, but for me it was a mixture of awe and some strange primal fear. The sun went out and even though my mind knew why, my body lost it and panicked.

Solar eclipse in 2024

On April 8th, a total solar eclipse will pass over Mexico, the United States, and Canada. Our special series covers everything you need to know, from how and when to see a solar eclipse to the strangest solar eclipse experience of all time.

This seems to be a fairly common reaction, not just in humans. Researchers who studied animals during past total solar eclipses found that while some animals simply finished their evening routine early, many showed signs of anxiety and were aimless during total solar eclipses. I discovered that they run and huddle together.

Then, just a few minutes later, the total star will retreat as quickly as it arrived. The shadows rush away, the sun comes out again, and the birds and insects sing again. Astronomers look up from their solar telescopes, dazed but excited by the treasure trove of data they’ve collected.

Humans have been observing solar eclipses for thousands of years, and we’ve learned some very interesting things. When the sun’s disc is covered by the moon, its faint corona becomes visible, making solar eclipses the perfect time to study the sun’s outer reaches. For example, scientists first discovered helium during a total solar eclipse. Solar eclipses are also a great time to observe the plumes of radiation and material emitted from the sun’s surface through the corona. The coronavirus itself is very strange, and there is still much to learn about how it works. Despite being far removed from the sun’s core fusion, the corona is millions of degrees hotter than the sun’s surface, and we still don’t know why.

Even if you haven’t studied the sun’s mysterious layers, it’s worth watching a total solar eclipse. More than 100 years ago, newspaper editors got it right. More or less, you will be confused.