Why Study Solar Eclipses?
Humans have been studying solar eclipses for thousands of years, looking with eyes, telescopes, cameras and high-tech instruments.
So what’s left to study, especially now that we can observe the Sun with spacecraft and orbiting telescopes? Surprisingly, scientists say researchers and students can still learn new facts about the Sun from right here on Earth–especially during total solar eclipses.
Structures in the solar corona are visible in polarized light, such as the dark prominence that can be seen on the bottom right of the Sun captured during the 2017 eclipse from Tetonia, Idaho. (David Elmore and Richard Kautz)
During the last US total solar eclipse, in August 2017, scientists, teachers and students across the country engaged in scientific studies that took advantage of the window of “totality,” the brief minutes when the Moon blocks out the Sun’s light and skies go dark.
NASA's Earth Polychromatic Imaging Camera (EPIC) tracked the path of the total solar eclipse across North America on Aug. 21, 2017. NASA scientists will use these observations to better understand how clouds affect Earth’s energy balance. (NASA Goddard/DSCOVR/EPIC)
One team of researchers chased the eclipse’s path in a high-speed jet while measuring the origins of the “solar wind.” Others tried to get new data on the Sun’s corona. And the Exploratorium gave millions of viewers a glimpse of what it’s like to look at the Eclipse through a powerful telescope.
A team of NASA-funded scientists led by Amir Caspi of the Southwest Research Institute used telescopes mounted on a pair of NASA jets to extend their observation time of the Sun’s corona, seen here in green-wavelength visible light. (NASA/SwRI/Amir Caspi/Dan Seaton)
One of the WB-57F jets that observed the total eclipse for about three and a half minutes (compared to two minutes as seen from the Earth's surface) as they fly over Missouri, Illinois, and Tennessee. (Amir Caspi/NASA)
“Solar eclipses are one of the most spectacular natural events one can experience on Earth,” says Rob Semper, chief science officer of the Exploratorium.“But more than that,” he said, “They also offer scientists a great opportunity to learn more about our sun and the universe. In the past, solar eclipses have given us proof of Einstein’s theory of general relativity, provided the conditions to support the discovery of the element helium and even helped demonstrate that the earth was round!
Take the Sun’s corona–the top layer of the Sun’s inner atmosphere. Because the sun's surface is so bright, it is normally impossible to see the much fainter corona. But during totality, the moon almost completely blocks light from the Sun’s surface. When that happens, the inner corona can be easily seen–and scientists then race to observe it during the few minutes of totality. During the eclipse, the moon blocks the Sun's photosphere surface so perfectly that you can see even more of the inner corona than you can see from satellites which use a blocking disk to make artificial eclipses.
There are still mysteries surrounding the corona: Why, for example, is it so hot? The corona is over 1.8 million degrees Fahrenheit–yet the sun’s surface is a much cooler 10,000 F. During the 2017 eclipse, researchers found that even when the Sun is covered by sunspots and other gigantic surface phenomenon, the corona’s temperature stays constant. Scientists are still trying to figure out why.
Special filters enable scientists to measure different temperatures in the corona during total solar eclipses, such as this one seen in Mitchell, Oregon, on August 21, 2017. The red light is emitted by charged iron particles at 1.8 million degrees Fahrenheit and the green are those at 3.6 million degrees Fahrenheit. ( Miloslav Druckmuller)
Elsewhere on eclipse day, Smithsonian researchers took to the skies in a high-flying Gulfstream jet from the National Center for Atmospheric Research to study the magnetic origins of the solar wind. Flying at over 880 km/h, the researchers were able to eke out extra time in totality to make their observations. Learning about the solar wind is crucial, as the particles emitted from the sun can impact radio and satellite communications on Earth.
And for those who could not be near the path of totality, the Exploratorium sent an observation team to Oregon and Wyoming equipped with high-powered telescopes and video equipment that allowed visitors to our website to get the same telescopic view of the eclipse that scientists on site were getting.
That’s just a taste of what researchers took away from the 2017 eclipse. When the next great American total solar eclipse darkens skies on April 8, 2024, you can bet researchers will have a full plate of experiments lined up to study our closest star.
Total solar eclipses give astronomers the opportunity to view the stars surrounding the sun in a whole new light. Einstein predicted that light should be bent by gravity, and Sir Arthur Eddington led an expedition to photograph the 1919 total eclipse of the sun. The photographs he took revealed stars whose light had passed near the sun, and their positions showed that the light had been bent exactly as Einstein had predicted.