In 1913, Albert Einstein sent a letter to George Ellery Hale, founder of the Mount Wilson Observatory, high in the mountains above Pasadena, asking about a research method that could be used to prove his theory of relativity.
According to Einstein’s theory, gravity from a very massive object, like the sun, should bend light around its mass like a lens.
In order to prove this theory, someone needed to observe an object, such as a star, right over the sun’s shoulder. The problem was figuring out how to observe the sun and stars at the same time.
Enter eclipses.
Six years after Einstein’s letter, astronomers Frank Watson Dyson and Arthur Stanley Eddington proved Einstein’s theory during an eclipse over the island of Principe, off the west coast of Africa.
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Many generations later, scientists have been giddy lately, as Monday’s total solar eclipse approaches.
And by just after 11 a.m. PDT on Monday, they’ll be beyond giddy. That’s when the Earth’s familiar Sun will begin disappearing for people in North America as the total solar eclipse enters the continent through Mexico’s Pacific Coast.
From there, the “path of totality”, the band where the sun is completely blocked from view, will cut diagonally across the continent, delighting U.S. viewers from Texas to Maine. All told, the totality will pass over 13 U.S. states, and at least a partial eclipse will be visible from all 50, within eyeshot (though do not look at it directly) of 99% of the U.S. population.
Joel Zinn, assistant professor in Cal State Long Beach’s Department of Physics and Astronomy, looks skyward on Friday, Apr. 5, 2024, with the special glasses and Coronado solar telescope he’ll use during Monday’s viewing party of the solar eclipse at the university. (Photo by Howard Freshman, Contributing Photographer)
For scientists, eclipses open up unique research opportunities, which conjure up the great questions of space and light.
For proving Einstein’s theory of general relativity, of course, an eclipse was a powerful place to start.
“Historically, it was the only way that you could observe certain parts of the Sun, simply because the sun is so very bright,” said Christopher Burns, a volunteer telescope operator at Mount Wilson Observatory and research associate at the Observatories at Carnegie Science. “You can’t look directly at it, obviously. And any telescope that you try to point at it is going to be completely overwhelmed.
“If you’ve got some telescopes, you can measure the positions of stars that are now visible in the dark sky during the total eclipse,” Burns explained.
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Then a scientist could return later, at night, and view the stars without the sun’s influence. If the positions changed, Burns explained, then Einstein’s prediction was correct.
Burns said that eclipse watching can be an addictive experience for some.
“A lot of people get addicted to this. And so they see their first eclipse and then they start chasing eclipses, we call them eclipse chasers,” Burns said.
Some of these eclipse chasers may already have their travel plans lined up. On Oct. 2, 2024, an annular eclipse will cross over South America and a partial eclipse will be visible from spots in South America, North America, the Pacific and Atlantic Oceans and Antarctica. To see the next total eclipse, on Aug. 12, 2024, foreign enthusiasts will need to travel to Greenland, Iceland, Spain, Russia or Portugal.
Solar eclipses provide a rare opportunity when scientists and astronomers join people with little interest in the cosmos, all staring at the same celestial phenomenon for a few minutes.
At a JPL eclipse-viewing event at the Austin Public Central Library, Michael Saing, a JPL systems engineer and amateur astronomer, will be sharing his passion for astronomy with a talk and live demonstration of what the eclipse looks like through a Hydrogen-Alpha telescope. Such a devise allows gazers to see in detail surface features of the sun, such as spots, prominences and flares.
Saing understands how powerful a single glimpse into the stars can be. While pursuing a law degree, Saing signed up for his first astronomy class at the end of his time in community college.
“That blew me away,” Saing recalled. “So I changed my major right away to aerospace engineering.”
FILE – The moon covers the sun during a total solar eclipse Monday, Aug. 21, 2017, in Cerulean, Ky. On April 8, 2024, the sun will pull another disappearing act across parts of Mexico, the United States and Canada, turning day into night for as much as 4 minutes, 28 seconds. (AP Photo/Timothy D. Easley, File)
One night, his professor brought out a telescope, allowing the class to see Jupiter and Saturn.
“He didn’t have to, but he did that,” Saing reminisced. “That’s kind of what got me started.”
Now, Saing says it’s important for him to share his equipment and knowledge with others.
“With this particular event, it means a lot to me that I can share my passion with other people, hoping that you know, it also kind of brings them into the STEM field as well,” Saing explained.
In short, for those who study space, Monday will, in effect a bonanza.
They’ll photograph the sun’s outer crownlike atmosphere, or corona, as the moon passes between the sun and Earth, blotting out sunlight for up to 4 minutes and 28 seconds. They’ll observe the quieting of birds and other animals as midday darkness falls. They’ll also measure dropping temperatures, monitor clouds and use ham radios to gauge communication disruptions.
Even rockets will blast off with science instruments into the electrically charged portion of the atmosphere near the edge of space known as the ionosphere.
More than 600 weather balloons will be launched by college students along the track, providing livestreams while studying atmospheric changes. Cloudy skies shouldn’t matter.
Plus, there are two new spacecraft out there studying the sun: NASA’s Parker Solar Probe and the European Space Agency and NASA’s Solar Orbiter. They’ll join other spacecraft on eclipse duty, including the International Space Station and its astronauts.
So, yes, today’s scientists still rely on eclipses to make observations of the sun. But they are also excited about sharing that knowledge.
Marin Anderson, astrophysicist, radio astronomer and research scientist at NASA’s Jet Propulsion Laboratory (JPL)Anderson helps educate students and citizen scientists using the Goldstone Apple Valley Radio Telescope (GAVRT) to map the sun. On Monday, the GAVRT team will be hosting a public, live-streamed webinar to demonstrate how eclipses can be used to aid solar research.
Left to right in 1931: Walter Sydney Adams, Albert Abraham Michelson, Walther Mayer, Albert Einstein, Max Farrand, Robert Andrews Millikan (president of Caltech).Date: 1931 Repository: Smithsonian Institution Libraries
Scientists studying the sun are interested in better understanding its corona, the outer atmosphere of the sun. According to Anderson the “corona is a really important part of the Sun in terms of producing magnetic activity”, which produces “space weather events”, bursts of electromagnetic radiation that can wreak havoc on Earth’s infrastructure, satellites, and astronauts. Among other things, scientists are interested in better forecasting these events.
During an eclipse, as the moon transits across the sun’s path, it slowly covers and uncovers the sun’s active regions, allowing scientists to take readings with much higher resolution.
At these times, the clarity of radio telescope readings, called angular resolution, improves by more than two orders of magnitude.
“We can see the structure of the magnetic fields in the sun’s outer atmosphere, in that corona, more than 100 times better than we would be able to see it during standard, non-eclipse observations,” Anderson said.
Anderson is still struck by just how much of a moment this is.
“It’s a coincidence that we happen to be on a planet with a Moon that’s about 400 times smaller than our star, but that our star is about 400 times further away,” Anderson explained.
“And so we just so happened to live on this planet. At this moment in time, when we get to experience the moon being exactly the same size in the sky as the sun.”
According to Anderson, in around a billion years, the moon will have drifted far enough from Earth that total eclipses will be a thing of the past, so get ‘em while we got ‘em.
Related links
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The Associated Press contributed to this article.