UW News

April 4, 2024

Q&A: Eclipses aren’t just good for jaw-dropping views — they’re also opportunities for stellar science, says UW astronomer

UW News

Image of the total solar eclipse of Aug. 21, 2017, taken from the Warm Springs Reservation in Oregon.University of Washington

The total solar eclipse on April 8 will give fortunate viewers across North America the chance to see something rare and spectacular. It will be the first total eclipse visible in Mexico since 1991, and in Canada since 1979. The continental U.S. won’t see another for 20 years.

As people in and near the eclipse’s path of totality check weather reports and obtain safe viewing glasses, scientists are also getting ready. Eclipses past and present aren’t just opportunities for incredible sights. Generations of researchers have used them to study phenomena ranging from the sun itself to the fabric of the universe.

Emily Levesque, a University of Washington associate professor of astronomy, is an expert on stars, particularly ones that are much larger, more violent and shorter-lived than the sun. Levesque is also an author and lecturer on the history of observational astronomy. Her book, “The Last Stargazers: The Enduring Story of Astronomy’s Vanishing Explorers,” was published in 2020 and her filmed lecture series, “Great Heroes and Discoveries of Astronomy,” is available on Wondrium.

UW News sat down with Levesque to talk about some of the things scientists — past and present — have learned from solar eclipses.

Why are total eclipses such a major event for scientists?

Emily Levesque: In a total solar eclipse, the sun is being perfectly covered by the moon. That allows us to see and measure things that are normally blocked by the incredibly bright surface of the sun. Once you remove that intense light, a lot of great observations are possible.

What sorts of observations are made possible by the eclipse?

EL: For people who study the physics of the sun, a total eclipse is the best chance of observing the sun’s corona directly from Earth. The corona is this stream of white-hot plasma — very hot, as much as 2 million degrees Fahrenheit — that’s constantly being torn off the edges of the sun and sprayed many thousands of miles above the sun’s surface. Normally, the sun’s intense light obscures the corona. For anyone in the path of totality, during those few minutes where the moon’s disc completely obscures the sun, you can see those intricate details of the corona. It’s really incredible. And for a scientist, it’s a great moment to gather data.

Do you mean scientists who are in the path of totality when the eclipse occurs?

EL: Yes. But not just scientists who happen to live in or near the path of totality. I have colleagues that have pioneered eclipse chasing. I’ve heard great stories about their adventures on expeditions all over the world to observe solar eclipses, like trying to see one in northern Norway — where they had to receive polar bear safety training — or traveling to Tatakoto, a tiny atoll in French Polynesia. There’s a total solar eclipse on average about once every 18 months, but the vast majority of Earth’s surface is water. So they travel around the world to take their measurements where and when they can.

What sorts of measurements can astronomers make during these trips?

EL: These observers don’t need huge telescopes. But they need telescopes with a lot of fancy equipment attached to them — like a fancy digital camera instead of an eyepiece. Or a telescope with a spectrograph. A spectrograph is a device that can capture light and separate it by color. Researchers can analyze the data to figure out the chemical composition of the corona. The corona is an incredibly complex structure. It’s influenced by the sun’s magnetic field, its rotation and a host of other factors. There’s a lot that’s not known about the corona and how it impacts phenomena like solar flares, which can interfere with our satellites and communication.

Setting aside the corona, what else have scientists used eclipses to study?

EL: One weird and infamous example is that scientists tested and proved one of Einstein’s theories during an eclipse. Einstein’s theory of relativity explains the relationship between space and time and gravity. Today, you’ll often hear people talk about spacetime — the inextricable link between space and time that is the fabric of the universe. If you think of spacetime as a flat sheet, Einstein’s theory is that, if you add gravity to it — especially a lot of gravity — that sheet becomes curved, like if you had dropped a bowling ball on that sheet.

Einstein’s theory states that, for something massive like the sun, spacetime around it should be curved just a little bit — and that should bend the path of light from other stars passing near the sun. Einstein published this theory in 1915 using some amazing and beautiful mathematics. He also imagined this gorgeous experiment of proving it by making observations during an eclipse of stars whose light passes close to the sun. The sun should be bending that light just a little bit, which would make their position appear to shift very slightly. Normally, it would be impossible to see those stars and measure their positions. But, you can do it during an eclipse, when the sun is completely covered.

Did Einstein follow through with that experiment?

EL: No, but his theories led to international collaborations among scientists to use a solar eclipse to test the theory of relativity. It’s really amazing because this is happening during and immediately after World War I. There were some attempts that failed due to weather conditions during the eclipse and political strife. But finally, during a solar eclipse in 1919, a British scientist named Sir Arthur Eddington led a team that took the right measurements during those few minutes of totality — measurements of those stars positioned nearest to the sun relative to Earth — and showed that Einstein was correct!

What advice do you have for anyone in the path of totality?

EL: Have fun and be safe — and especially make sure you have viewing glasses from reputable sources before looking at the sun prior to totality. If there’s an astronomy club near you, or a university or college with an astronomy club, see if they’re holding a viewing event and join them. But even for people who aren’t in the path of totality, there will be a lot to see — again, using safe and reputable viewing glasses. From Seattle, about 20% of the sun will be obscured. It will look like someone took a bite out of it. It’s an incredible event!

For more information, contact Levesque at emsque@uw.edu.