Planetary Sciences News

Sixteen Eclipse Studies That Illuminate Science from the Shadow

From jets that will chase the Moon’s shadow to a telescope designed to mimic the eyes of a mantis shrimp, projects across the United States will pack science into mere minutes when day turns to dark.

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How much science can researchers cram into 90 minutes? On 21 August, as the Moon blocks out the Sun and its shadow races across the United States, the world will find out. Hundreds of scientists and citizen scientists will transmit radio signals, release high-altitude balloons, take thousands of pictures, and even chase the Moon’s shadow in planes to collect as much data as possible.

Research jets during a solar eclipse.
During the upcoming total solar eclipse, a team of scientists will observe the solar corona using NASA’s WB-57F research aircraft. This composite photo comes from the 2015 total solar eclipse seen at the Faroe Islands. Credits: : NASA/ Faroe Islands/SwRI

Scientists will study the Sun’s corona, which is usually too dim to observe compared to the Sun’s bright light. Amateur ham radio operators will send transmissions to each other to study how Earth’s outer sheath of plasma shrinks and grows in response to the quickly diminishing solar energy brought on by the eclipse. Earth-orbiting satellites will peer back at our planet to monitor changes in incoming solar radiation. Citizen scientists with apps will observe how cloud cover and temperatures change and even how animals and plants behave during the small window of shadow.

Eclipse science projects radiate from three realms: space, the sky, and on the ground. Here are just 16 of the many scientific projects that will illuminate solar and terrestrial science during the short span of transiting darkness.

The Eclipse from Space

1. X-ray explosions. The Hinode satellite, operated by NASA, the Japan Aerospace Exploration Agency, and agencies in the United Kingdom, will watch from space as the Moon passes in front of the Sun. Hinode’s instruments will be poised to observe the solar corona, the Sun’s magnetic field, and jets of X-rays that explode from the Sun’s surface. Researchers still aren’t sure what drives the Sun’s powerful eruptions, but Hinode’s observations will help them solve this mystery.
2. Defining the Moon’s shadow. Thanks to instruments on the Lunar Reconnaissance Orbiter (LRO), we know the precise topography of the Moon: the height of its highlands, the depth of its mare, the shape of the ridges that rim impact craters. With this information, scientists have plotted in fine detail the rough edges of the expected shadow that the Moon will cast on Earth during the eclipse, all along its path.

Knowing the shape of the shadow as it moves is also helping scientists locate places where dots of sunlight known as “Baily’s beads” will peep through during the eclipse thanks to concavities in the lunar shadow. During the eclipse, these predictions will be ground-truthed: LRO cameras will turn around and point at Earth to image the path of the Moon’s shadow.

SOHO-coronagraph
An image of coronal mass ejections from the Sun in 2010. NASA’s Solar and Heliospheric Observatory (SOHO) uses coronagraphs to artificially block out the Sun to observe the corona. However, these coronagraphs also block out the lowest layer of the Sun’s corona, an area of great interest. During the solar eclipse, the Moon will mask the solar disk but leave behind the entire corona, enabling scientists to study those otherwise difficult to observe layers. Credit: NASA/ESA

3. Simulated eclipse. The joint European Space Agency/NASA Solar and Heliospheric Observatory (SOHO) will not see the Moon cross over the Sun. But instruments aboard SOHO can simulate an eclipse using a coronagraph, an opaque circle placed into a telescope’s view, masking the Sun’s brightness.

There’s a catch, however. Coronagraphs produce diffraction patterns just beyond the edge of the opaque disk and are designed to be larger than the area illuminated by the Sun to protect instruments. Thus, they blur the region very close to the solar surface, where space weather originates.

Images taken on the ground of the total eclipse, however, won’t have such problems, but they won’t have the image-processing capabilities or the space vantage of a powerful satellite. So the full suite of coronal data captured by SOHO can then be complemented with images of the corona taken from the ground to create a more complete picture of the corona than either platform can do alone.

4. A peek into the chromosphere. The Interface Region Imaging Spectrograph (IRIS), one of NASA’s Small Explorer missions, will see the Moon transit across the Sun more than once on Monday as it moves in its polar orbit. During these transits, IRIS will capture images of the Sun’s chromosphere, which is its lower atmosphere. The chromosphere sits just above the photosphere and below the corona.

Like the corona, the chromosphere is much dimmer than the photosphere and can be seen only during a total solar eclipse. At its vantage in space, “IRIS will be sensitive to solar material at temperatures that cannot be seen from the ground, for example, the material in the lower atmosphere at the interface between the chromosphere and corona, which is around 100,000 K,” NASA reports.

5. Clouds’ role in regulating Earth’s energy. A team of researchers from NASA and Morgan State University in Baltimore, Md., will be analyzing data from the Deep Space Climate Observatory (DSCOVR), the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the Terra satellite, and ground observations before, during, and after the eclipse. Their goal is to collect enough information to simulate the event using what’s known as a 3-D radiative transfer model. Through such a simulation, scientists hope to improve estimates of how much solar energy reaches the ground and propagates across the planet.

Here’s the clever part: The model can treat the shadow of the Moon like the shadow of a cloud. “Even though the Moon blocking the Sun during a solar eclipse and clouds blocking sunlight to Earth’s surface are two different phenomena, both require similar mathematical calculations to accurately understand their effects,” NASA reports. By comparing this shadow with other actual shadows of thick blanketing clouds, scientists hope to tease out how clouds scatter solar energy in three dimensions, knowledge lacking from current climate models.

The Eclipse Fleet: Instruments in the Sky

6. Searching for nanoflares. Two specially equipped NASA jets will chase the shadow of the Moon over the United States as it passes between Earth and the Sun. For these planes’ pilots and the twin telescopes mounted on their planes’ noses, the eclipse will last more than 7 minutes. What’s more, they’ll be flying at an altitude of 15 kilometers, well into the stratosphere. Up there, “the sky is 20–30 times darker than as seen from the ground,” NASA reports. “There’s much less atmospheric turbulence, allowing fine structures and motions in the Sun’s corona to be visible.”

At this vantage, the telescopes will be poised to capture the clearest images of the corona ever taken. Scientists want such images so that they can come closer to solving some persistent solar mysteries. For example, why is the corona superhot, with temperatures reaching more than 1 million kelvins, while at best the surface of the Sun reaches a mere 6,000 kelvins? One theory is that microexplosions called nanoflares—bursts too small to have ever been individually captured before—might push heat into the corona. Scientists hope the new highly detailed images will help them to witness one of these elusive mini solar flares.

7. Magnetic mysteries. Nanoflares are just one of many ideas for how the corona gets so hot. Heating mechanisms are varied, but they all involve energy in the corona’s magnetic field somehow converting to heat. Thus, solving the mystery of how the corona heats will require detailed studies of the corona’s magnetic field.

The key to this lies in harnessing faint coronal light from the infrared spectrum at wavelengths known to be sensitive to magnetic field dynamics. Thanks to new technology, these faint infrared signals can now be detected by specially built instruments. But these instruments can’t be positioned on the ground—water and other atmospheric gases distort infrared wavelengths from the Sun.

A group of researchers from the Harvard-Smithsonian Center for Astrophysics and the National Center for Atmospheric Research has teamed up to fly these sensitive instruments on a Gulfstream V jet owned by the National Science Foundation. The jet will also fly at an altitude of 15 kilometers and will orient instruments toward the solar eclipse for 4 minutes as it chases the Moon’s shadow above southwest Kentucky. Researchers hope that data collected will also help to pinpoint how the Sun’s atmosphere generates adverse space weather.

Students with high altitude balloon
During the solar eclipse on 21 August, students from the Eclipse Ballooning Project will release high-altitude balloons like this one. They will also be live-streaming their launches and feeds from cameras mounted on the balloons. Credit: Kelly Gorham /Montana State University

8. Balloons launches. Many groups will use high-altitude balloons to observe and study the eclipse. A Montana State University–led group called the Eclipse Ballooning Project will launch 57 balloons in 25 locations across totality. Each balloon will be able to transmit video and still images of the eclipse.

Meanwhile, students from a group called Earth to Sky Calculus, based in Bishop, Calif., will also be launching balloons. During the eclipse, Earth to Sky Calculus members, along with groups they’ve trained across the country, will launch at least a dozen balloons from the path of totality. Their goal is to study cosmic rays and their effect on Earth’s magnetic field, said Tony Phillips, a science writer at NASA and leader of the student group. Although they don’t expect the eclipse to have any particular effect on cosmic rays, the event “gives us an opportunity, or rather an excuse, to map out variations in Earth’s magnetic shielding against cosmic rays from one end of the country to the other,” Phillips told Eos. Some of the balloons will also be affixed with 360° cameras to capture the entire eclipse.

Science from the Ground

9. Just how hot is the corona? A team of scientists dubbed the Solar Wind Sherpas, with leadership from Hawaii’s Institute for Astronomy, will venture to select sites in Oregon, Idaho, Wyoming, and Nebraska to study the temperature of the Sun’s corona. The team will point specially built spectrometers and polarizers at the eclipse to study the nature of light emitted from various ionized elements in the corona. The temperature of the corona is dependent on the distribution of the ionized elements they find. These temperatures, in turn, are governed by the Sun’s magnetic field. Thus, finely scaled maps of coronal temperatures can help reveal information on the corona’s magnetic field, information crucial to resolving why the corona is so much hotter than the surface of the Sun.
10. The colors of the corona. Perched on a mountaintop near Casper, Wyo., scientists from Colorado’s High Altitude Observatory (HAO) will point a newly developed spectrometer at the Sun during the eclipse.

The spectrometer, dubbed PolarCam, is “inspired by an ocean animal called the mantis shrimp,” according to an HAO blog post. “Humans have three photoreceptors in our eyes, sensitive to red, green, and blue. The mantis shrimp has sixteen! Not only can it see more colors, but it can detect polarized light. The PolarCam uses the same vision methods.”

PolarCam will collect light and split it into various composite wavelengths, seeking out how light is distributed across the entire spectrum of the corona. The team will compare results to spectral data of the corona captured by satellites during the eclipse as a proof of concept for this camera’s use in future space missions. Ultimately, the data will help scientists to better model and predict space weather, which begins in the corona.

11. Building efficient instruments. A group of NASA scientists will gather in Oregon to test a newly developed camera on coronal light. The camera uses thousands of mini polarization filters to capture polarized light in different directions at the same time that other filters harness various wavelengths of light from the corona. The technique speeds up image process times by 50%. More details of the project are in the video below, recorded just before a total solar eclipse in March 2016.

12. What can the corona tell us about the solar cycle? Scientists from Massachusetts’s Williams College will travel to Oregon to focus their telescopes on defining the shape of the corona, which is confined by the corona’s magnetic field. Using these observations along with data from past eclipses, the researchers hope to determine whether the observed coronal shape reveals information on the exact phase of the 11-year sunspot cycle.
13. The shrinking and expanding ionosphere. When the Sun’s ultraviolet light reaches Earth, its energy ionizes molecules in the upper reaches of Earth’s atmosphere, creating the ionosphere, which stretches 60–1000 kilometers above the planet’s surface. As the Moon briefly blocks out the sun’s light, the ionosphere will shrink and grow over a relatively short period of time. To study the effects of the eclipse, researchers can use radio transmissions to bounce radio waves off the ionosphere and detect how their properties change before, during, and after the eclipse.

Researchers from the Georgia Institute of Technology will be looking at the lowest and least dense part of the ionosphere, called the D region. This region, closest to Earth’s surface but too high for balloons to reach, is important for certain kinds of telecommunications from military, naval, and engineering operations. For these experiments, researchers will probe the ionosphere using radio waves at 300 kilohertz, a low frequency never before used to sense the ionosphere.

Traditionally, researchers would use very low frequency radio waves—between 300 hertz and 30 kilohertz—to study the ionosphere, but those radio waves bounce off the ionosphere in many different paths, so “disentangling them is very difficult,” Morris Cohen, an electrical engineer at Georgia Tech who will lead the research, told Eos. Three hundred kilohertz falls into the low-frequency spectrum of radio waves, which reflect off the ionosphere more efficiently, allowing a more direct measurement, he said.

14. Ham radios users, unite! Ionosphere data will also be bolstered by a network of amateur ham radio operators called the Ham Radio Science Citizen Investigation. Across the nation, these citizen scientists will transmit messages, sending radio signals up into the ionosphere. With data from radio operators and from receiving networks like the Reverse Beacon Network (a network of receivers listening to transmissions) scientists will be able to detect how the ionosphere changes across time and space before, during, and after the eclipse.

15. A line of telescopes in the path of totality. The National Solar Observatory, meanwhile, will harness the power of 68 telescopes to study the Sun’s corona as it shines out from behind the Moon in a citizen science project called the Citizen CATE Experiment (CATE stands for Citizen Continental-America Telescopic Eclipse). Across the United States, amateur astronomers, student groups, and universities will operate these telescopes; during totality, they’ll each take more than 1,000 images, offering 90 minutes of continuous, high-resolution coverage. See their exact positions in the map below.

Scientists will use the data collected by this group to examine fine details of coronal dynamics, including any plumes of plasma.

16. There’s an app for that. If you’re not part of an official group, there are still citizen science activities you can do on your own! For instance, an app called GLOBE Observer allows anyone to measure how cloud cover might change during the eclipse. Or you could use the iNaturalist app to observe how animal and plant behavior changes (total eclipses are known for quieting birds and causing flowers to prematurely close).

Meanwhile, thousands of people from across totality will use digital cameras and smartphones to capture images of the eclipse for the Eclipse Megamovie Project. These images will be stitched together by a team at the University of California in Berkeley to create “a movie of the entire eclipse from coast to coast,” the team wrote. Not only will these images help scientists study the eclipse, but they will also help foster wonder and excitement for a rare natural event, they said.

—JoAnna Wendel (@JoAnnaScience), Staff Writer; and Mohi Kumar (@scimohi), Scientific Content Editor

Citation: Wendel, J., and M. Kumar (2017), Sixteen eclipse studies that illuminate science from the shadow, Eos, 98, https://doi.org/10.1029/2017EO080063. Published on 17 August 2017.
© 2017. The authors. CC BY-NC-ND 3.0