For six decades, Williams College astronomy professor Jay Pasachoff has crisscrossed the globe—from Manitoba to Papua New Guinea—to bear witness to totality, when our Moon completely blots out the Sun. But on August 21, when the Great American Eclipse crosses the United States, he won't travel far to see the phenomenon that he's spent so much of his life chasing.
"I've seen 65 solar eclipses so far," says Pasachoff. "Sure hope it will be 66."
Pasachoff started studying solar eclipses during the Eisenhower administration, but because they are so short and so rare—a brief few minutes that happens somewhere on the planet about every 18 months—there is still much to learn from total solar eclipses. He and his team of professionals and students are planning on doing a "panoply of observations," including on the part of the Sun that's usually invisible to the naked eye—the corona, the outermost part of our star's atmosphere.
"We hope to learn a lot about the different aspects of the solar corona," explains Pasachoff, "about the motions of the corona, the heating of the corona, and the overall shape of the corona."
He's not the only one. NASA is supporting and sponsoring 11 missions that will use 21st century tools such as high-definition video cameras, infrared telescopes, and Fourier Transform Spectrometers, with the hopes that they will provide answers to questions that have been pondered by astronomers for millennia.
The Corona Conundrum
On a normal day, we can see only the photosphere, the approximately 300-kilometer (186 mi.) thick layer of gas that surrounds our Sun. It's also about 100,000 to a million times brighter than the corona. Yet while the photosphere can reach a balmy 10,000 degrees Fahrenheit, but it's the corona that's a real scorcher at about 3.5 million degrees Fahrenheit.
Why? No one really knows, in part because the corona is so often hidden from view. While a coronagraph can create an artificial, mini-eclipse, it can not emulate the total darkness of the moon actually blocking the Sun. A total solar eclipse offers a fleeting but clear look at the corona, which is an irreplaceable opportunity for scientists.
In the morning of August 21, Amir Caspi and his fellow researchers from the Southwest Research Institute in Boulder, CO, will be observing the flight of two NASA WB-57 aircraft from the mission operations center at Ellington Field in Houston near Johnson Space Center. The planes will take off from Houston, ascend to 50,000 feet, and make their way to the path of totality where they will ultimately fly over Carbondale, IL.
Flying at speeds up to 470 miles per hour, these twin planes will take images and measurements of the Sun's corona in both visible and infrared light. This will be done by a two-telescope system called DyNAMITE, developed by Southern Research in Birmingham, Alabama,that snaps images at 30 frames per second.
"[The WB-57s] are basically converted bombers that NASA is using as research aircraft," Caspi told Popular Mechanics, "and [DyNAMITE] was originally built...to observe rocket launches. This is the first time this instrument is being used for scientific, astronomical research." Because of their height and speed, the two planes will be able to tag-team and collect about eight minutes worth of data—more than three times what researchers will get on the ground.
"Classical thermodynamics suggest that you shouldn't have something that hot on top of something that cool," says Caspi, "What we know is happening is that energy is getting into the corona and that energy is heating it up. We think it's coming from the coronal magnetic field but how it is being delivered is something we don't quite understand."
Riding the (Infrared) Waves
Even a small amount of solar activity millions of miles away can have an enormous impact on Earth's climate, particularly on trade winds and precipitation. Activity like solar flares, coronal mass ejections, and eruptions—often referred to collectively as "space weather"—can wreck havoc on our tech, leading to radio blackouts, damage to electrical grids, and even knocking out GPS satellites.
From a trailer in Casper, WY, a small town directly in the eclipse's path, another NASA-funded study will point a spectrometer called the NCAR Airborne Interferometer at the corona, using infrared light to measure its intensity. This is the first time an experiment like this has ever been done, and it could help us better understand of the behavior of the solar magnetic field, a prime contributor to solar activity. This information could help scientists more accurately forecast space weather.
"The way it works is that we collect sunlight during the eclipse... then we use a beam splitter to send some of the light in one direction and some in a different direction," explains Paul Bryans of the National Center for Atmospheric Research who is leading the study, "Then we use mirrors to bring these two beams of light back together again. And that creates an interferogram. Then, we use that to determine the spectrum of the light."
While scientists have always had theoretical models of the Sun's magnetic field, measuring it directly could be a game changer in terms of predicting solar activity, something the federal government is already trying to figure out.
A Solar Golden Age
While the corona remains our Sun's biggest mystery, it's not the only one. Scientists are also interested in observing and recording how the Earth changes when the rays of the Sun fail to reach the surface.
During totality, the Moon passes in between the Sun and Earth and blocks all direct solar radiation in the path of totality. This will greatly impact our world's "radiation budget" because it will block incoming solar radiation and cause fluctuations in temperature, energy levels, and most obviously, light.
As the focus of two missions coordinated by NASA's Goddard Space Flight Center, these observations will be the first time that measurements from the ground and space taken during a solar eclipse will be used to calculate energy and radiation reaching Earth. It will also as provide the model for a 3D picture of the radiant energy in the Earth's atmosphere.
Also, the blacking out of the Sun means brighter planets as the resulting darkness will illuminate views of Venus, Jupiter, Mars and Mercury for casual observers and trained astronomers. Taking full advantage of the solar blackout, Caspi and his team will turn their instruments onboard the WB-57s towards Mercury to take high-resolution images of the solar system's smallest planet.
Beyond NASA-funded studies, there will be teams that will crowd source images to construct a full timeline of the eclipse crossing the country, others who will send out radio signals to determine changes in the Sun's ionosphere, and at least one zoo will observe how animals will react to daytime darkness.
The "Great American Eclipse" is more than just your average eclipse, it could set off a golden era of solar research. While the work done will hopefully lead to answers, it will also likely prompt even more questions about the giant yellow ball in the sky. With five more total solar eclipses cutting across the continent over the next four decades, there will be plenty more source material for the astronomers of tomorrow to study.
Pasachoff remembers observing his first solar eclipse when he was a college freshman and how he was cosmically drawn to the darkening display. He hopes the same will happen to his students.
"While we may not hear from them for decades," Pasachoff says, "[the eclipse] will be so spectacular that it can't help but inspire them."