On August 21, 2017, a wide swath of the US will experience a total solar eclipse, and two NASA WB-57 jets will chase the astronomical spectacle as it arcs across the country, sending thousands of images of the sun's outer atmosphere, known as the solar corona, and the planet Mercury.
The two high-altitude research jets will be equipped with optical sensors on the nose and images will be sent back to NASA and some will be used in real-time video streams. They will fly at 50,000 feet elevation in tandem at approximately 470 mph, the equivalent of Mach .78, one about 60 miles behind the other. The moon's shadow sweeps across the US at an average speed of about 1,500 mph. As the planes fly, the shadow will sweep over the trailing plane, then the lead plane. As one plane enters the area of totality, it will fly in it for about 3 minutes and 50 seconds before the sun begins to appear again. As that happens, the second plane, leading the first plane, will be entering the area of totality and have about 3 minutes and 40 seconds of totality before it ends, said Charlie Mallini, the WB-57 program manager for NASA.
"Between the two airplanes they will hopefully see between 7 to 8 minutes of totality," Mallini said. Observers on the ground will only experience a maximum of 2 minutes and 40.2 seconds of the eclipse, and that is if they are in the path of the longest expected totality, which is centered in Carbondale, IL. (The city of Hopkinsville, KY will be a very close second in totality with 2 minutes and 40.1 seconds.) Another benefit of observing the eclipse from 50,000 feet off the ground is that the planes will be flying above the clouds, so if there are weather issues, it won't affect NASA's ability to capture images.
NASA's optical sensors on the planes are third-generation AIRS/DyNAMITE and were developed by Southern Research, based in Birmingham, AL. They were originally designed to watch space shuttles during launch as a result of the Columbia space shuttle tragedy in 2003. Southern Research won the contract to start developing an imaging subsystem in 2004. This is the first time that the sensors have been used for a solar eclipse, or for any type of airborne astronomy, said John Wiseman, Southern Research's senior project leader for engineering.
How NASA's jets will capture data on the corona and Mercury
On the day of the eclipse, the two planes will launch from Ellington Field near NASA's Johnson Space Center in Houston and will fly over Missouri, Illinois and Kentucky and will then head southeast to Tennessee as the eclipse ends. The elevation will allow for improved image quality because the planes will be able to avoid the majority of the earth's atmosphere that distorts the view from the ground.
"What we're looking for is high speed motions in the solar corona that would be very difficult to detect from the ground," said Amir Caspi, principal investigator of the WB-57 eclipse chasing program and a senior research scientist at Southwest Research Institute (SwRI) in Boulder, CO, who is leading the scientific investigation.
Being in the air longer and having more time to observe the solar eclipse allows the scientists to have a better chance to detect faint motion in the solar corona. "The motion we're trying to observe might take more than 2-1/2 minutes to become observable. If it's a slow or dim motion that we're looking for, then in 2-1/2 minutes on the ground it might not move enough or be bright enough for someone to have seen it. But in the air with 7-1/2 minutes that gives us a much longer observing window and better sensitivity," Caspi said.
The team is trying to figure out why the solar corona is so hot. It's a few million degrees, compared to the visible surface of the sun, which is a few thousand degrees.
"That kind of temperature inversion is rather puzzling because when you think of atmospheres in a classic sense, temperatures get lower as you get higher. But in the corona, it's not that way. As you go from the photosphere up to the corona, the temperature drops a little bit and then shoots up millions of degrees. The classic ways we think of heat transfer-radiation, convection, conduction-they don't work very well in that environment. The corona isn't dense, it's very thin. You can see through it. It's so thin that conduction and convection don't work very well. We know that energy is getting into the corona to heat it, but the real question is how is that energy getting up there to heat it," Caspi explained.
"The second thing we're trying to address is why are the magnetic structures in the corona so stable for such long time periods. Why are they so smooth and well organized? They look like a freshly combed head of hair and not bedhead," Caspi said. "The modelling that we do of these magnetic structures suggests they should be getting tangled. Clearly, our models are incomplete. They're missing something, and we're trying to figure out what."
More than 14,000 solar eclipse images expected
The high-definition cameras on each plane will take 30 images per second during the total of 7 to 8 minutes of totality, for a possible total of more than 14,000 images. "These will be the clearest and highest quality observations of their kind of the solar corona to date," Caspi said.
Each plane carries two cameras. The first camera observes visible light and will have a special green filter that only allows a particular band of green light to get to the camera to give a better view of the hot magnetic structures in the corona. The second camera is an infrared camera, Caspi said.
The jets will also be taking images of the planet Mercury because typically Mercury is so close to the sun that specialized equipment is needed during the bright daytime sky, or it must be viewed before sunrise or after sunset, which means that layers of the earth's atmosphere are limiting the quality of the photos, Caspi said.
"During the eclipse, Mercury will be high in the sky and the sky will be relatively dark so we will be able to study Mercury with much higher quality than we can at other times. We will use the infrared camera to try to make the first ever heat map of Mercury's surface," Caspi said. "The reason we're interested in doing that is that by studying how Mercury's soil cools from its [Mercury's] really hot daytime to really cold night time teaches us about the properties of that soil—what it's made of, how dense it is—and that helps teach us how Mercury and other rocky planets were formed."
While a total solar eclipse appears somewhere on earth approximately once every 18 months, this particular eclipse is garnering more attention than most because it is the first to appear in the continental US since 1979, and the first time since 1918 that a total solar eclipse has crossed the entire US from the Pacific to the Atlantic.
Caspi said, "One of the things that I'm really hopeful for, and that I think a lot of the eclipse scientists and NASA are really hopeful for, is that this eclipse will spark the minds and imaginations of an entirely new generation of people. This is the first solar eclipse in the United States since 1979 and a lot of people in this country were not born or cognizant of the last solar eclipse. Technology has changed enormously since then. I'm personally hopeful that people will take this opportunity not only to get interested in this rare celestial event but also that it sparks a much deeper, longer lived interest and appreciation in science and astronomy."
The two high-altitude research jets will be equipped with optical sensors on the nose and images will be sent back to NASA and some will be used in real-time video streams. They will fly at 50,000 feet elevation in tandem at approximately 470 mph, the equivalent of Mach .78, one about 60 miles behind the other. The moon's shadow sweeps across the US at an average speed of about 1,500 mph. As the planes fly, the shadow will sweep over the trailing plane, then the lead plane. As one plane enters the area of totality, it will fly in it for about 3 minutes and 50 seconds before the sun begins to appear again. As that happens, the second plane, leading the first plane, will be entering the area of totality and have about 3 minutes and 40 seconds of totality before it ends, said Charlie Mallini, the WB-57 program manager for NASA.
"Between the two airplanes they will hopefully see between 7 to 8 minutes of totality," Mallini said. Observers on the ground will only experience a maximum of 2 minutes and 40.2 seconds of the eclipse, and that is if they are in the path of the longest expected totality, which is centered in Carbondale, IL. (The city of Hopkinsville, KY will be a very close second in totality with 2 minutes and 40.1 seconds.) Another benefit of observing the eclipse from 50,000 feet off the ground is that the planes will be flying above the clouds, so if there are weather issues, it won't affect NASA's ability to capture images.
NASA's optical sensors on the planes are third-generation AIRS/DyNAMITE and were developed by Southern Research, based in Birmingham, AL. They were originally designed to watch space shuttles during launch as a result of the Columbia space shuttle tragedy in 2003. Southern Research won the contract to start developing an imaging subsystem in 2004. This is the first time that the sensors have been used for a solar eclipse, or for any type of airborne astronomy, said John Wiseman, Southern Research's senior project leader for engineering.
How NASA's jets will capture data on the corona and Mercury
On the day of the eclipse, the two planes will launch from Ellington Field near NASA's Johnson Space Center in Houston and will fly over Missouri, Illinois and Kentucky and will then head southeast to Tennessee as the eclipse ends. The elevation will allow for improved image quality because the planes will be able to avoid the majority of the earth's atmosphere that distorts the view from the ground.
"What we're looking for is high speed motions in the solar corona that would be very difficult to detect from the ground," said Amir Caspi, principal investigator of the WB-57 eclipse chasing program and a senior research scientist at Southwest Research Institute (SwRI) in Boulder, CO, who is leading the scientific investigation.
Being in the air longer and having more time to observe the solar eclipse allows the scientists to have a better chance to detect faint motion in the solar corona. "The motion we're trying to observe might take more than 2-1/2 minutes to become observable. If it's a slow or dim motion that we're looking for, then in 2-1/2 minutes on the ground it might not move enough or be bright enough for someone to have seen it. But in the air with 7-1/2 minutes that gives us a much longer observing window and better sensitivity," Caspi said.
The team is trying to figure out why the solar corona is so hot. It's a few million degrees, compared to the visible surface of the sun, which is a few thousand degrees.
"That kind of temperature inversion is rather puzzling because when you think of atmospheres in a classic sense, temperatures get lower as you get higher. But in the corona, it's not that way. As you go from the photosphere up to the corona, the temperature drops a little bit and then shoots up millions of degrees. The classic ways we think of heat transfer-radiation, convection, conduction-they don't work very well in that environment. The corona isn't dense, it's very thin. You can see through it. It's so thin that conduction and convection don't work very well. We know that energy is getting into the corona to heat it, but the real question is how is that energy getting up there to heat it," Caspi explained.
"The second thing we're trying to address is why are the magnetic structures in the corona so stable for such long time periods. Why are they so smooth and well organized? They look like a freshly combed head of hair and not bedhead," Caspi said. "The modelling that we do of these magnetic structures suggests they should be getting tangled. Clearly, our models are incomplete. They're missing something, and we're trying to figure out what."
More than 14,000 solar eclipse images expected
The high-definition cameras on each plane will take 30 images per second during the total of 7 to 8 minutes of totality, for a possible total of more than 14,000 images. "These will be the clearest and highest quality observations of their kind of the solar corona to date," Caspi said.
Each plane carries two cameras. The first camera observes visible light and will have a special green filter that only allows a particular band of green light to get to the camera to give a better view of the hot magnetic structures in the corona. The second camera is an infrared camera, Caspi said.
The jets will also be taking images of the planet Mercury because typically Mercury is so close to the sun that specialized equipment is needed during the bright daytime sky, or it must be viewed before sunrise or after sunset, which means that layers of the earth's atmosphere are limiting the quality of the photos, Caspi said.
"During the eclipse, Mercury will be high in the sky and the sky will be relatively dark so we will be able to study Mercury with much higher quality than we can at other times. We will use the infrared camera to try to make the first ever heat map of Mercury's surface," Caspi said. "The reason we're interested in doing that is that by studying how Mercury's soil cools from its [Mercury's] really hot daytime to really cold night time teaches us about the properties of that soil—what it's made of, how dense it is—and that helps teach us how Mercury and other rocky planets were formed."
While a total solar eclipse appears somewhere on earth approximately once every 18 months, this particular eclipse is garnering more attention than most because it is the first to appear in the continental US since 1979, and the first time since 1918 that a total solar eclipse has crossed the entire US from the Pacific to the Atlantic.
Caspi said, "One of the things that I'm really hopeful for, and that I think a lot of the eclipse scientists and NASA are really hopeful for, is that this eclipse will spark the minds and imaginations of an entirely new generation of people. This is the first solar eclipse in the United States since 1979 and a lot of people in this country were not born or cognizant of the last solar eclipse. Technology has changed enormously since then. I'm personally hopeful that people will take this opportunity not only to get interested in this rare celestial event but also that it sparks a much deeper, longer lived interest and appreciation in science and astronomy."