Science from the ground

On August 21, 2017, a total solar eclipse will appear over a 70-mile wide path that crosses the country from Oregon to South Carolina. During the total eclipse, researchers will be able to see the faintest regions of the sun, as well as study the sun’s effects on Earth’s upper atmosphere.

The exceptionally long path over land of this total eclipse will provide an unprecedented opportunity for cross disciplinary studies of the sun, moon, Earth, and their interactions. Stars and planets will also be visible. NASA is supporting research using balloons, ground measurements, and planes that “chase” the eclipse, all of which can help scientists take continuous measurements of the sun and the eclipse’s effects on Earth for relatively long periods of time.

During a total eclipse, the lower parts of the sun's atmosphere, or corona, can be seen in a way that cannot completely be replicated by current human-made instruments.  The lower part of the corona is key to understanding many processes on the sun, including why the sun’s atmosphere is so much hotter than its surface, as well as the process by which the sun sends out a constant stream of solar material and radiation, which can cause changes in the nature of space and impact spacecraft, communications systems, and orbiting astronauts.

Total solar eclipses are also an opportunity to study Earth under uncommon conditions: In contrast to the global change in light that occurs every day at dusk and dawn, a solar eclipse changes illumination of Earth and its atmosphere only under a comparatively small region of the moon’s shadow. This localized blocking of solar energy is useful in evaluating our understanding of the sun’s effects -- temperature, for example -- on our atmosphere. Of particular interest is the impact on Earth’s upper atmosphere, where solar illumination is primarily responsible for the generation of a layer of charged particles called the ionosphere.

Eleven ground-based eclipse science missions and their locations are described here.


Studying the Sun’s Atmosphere

Chasing the 2017 Eclipse: Interdisciplinary Airborne Science from NASA's WB-57

Amir Caspi and Constantine Tsang of the Southwest Research Institute in Boulder, Colorado, will use the DyNAMITE visible and infrared telescopes on NASA’s twin WB-57 airplanes to get a unique look at both the sun and Mercury during the total solar eclipse. Flying in the stratosphere at 50,000 feet above the ground at up to 470 miles per hour, the two planes will tag- team to provide the researchers with a total of about 8 minutes of data during totality – a useful increase over the 2 minutes and 40 seconds afforded a single, stationary instrument on the ground. These observations are obtained at an altitude above 90% of Earth’s atmosphere, enabling exceptionally accurate measurements of the solar corona in visible and infrared light in order to better understand how energy moves throughout the sun’s atmosphere. Just after totality, when light is still low enough to allow the telescope to get a good look at Mercury, the instruments will turn their gaze from the solar corona to our solar system’s smallest planet for unprecedented observations of its surface in infrared light, which can be otherwise hindered by infrared radiation from the sun. Scientists hope these measurements will give new information about how Mercury’s surface temperature changes as its day turns to night, shedding light on the surface composition and properties.

The planes, which are operated out of NASA’s Johnston Space Center, will take off from Houston, Texas, and fly over Carbondale, Illinois and surrounding areas.

Citizen Science Approach to Measuring the Polarization of the Solar Corona

Padma Yanamandra-Fisher of the Space Science Insitute in Rancho Cucamonga, California, will lead an effort to take images of part of the sun’s atmosphere, the solar inner corona – visible only during total solar eclipses – in polarized light. Light becomes polarized as it passes through some kind of medium. The experiment will map the two-dimensional electron distribution in the inner solar corona, which will provide input for models that address the question of why the sun’s atmosphere, the corona, is so much hotter than its surface. The experiment, PACA_PolNet, builds on the work of a citizen science project known as Citizen CATE and will be conducted from two sites: Tetonia, Idaho and Carbondale, Illinois.

Studying the Corona in Infrared and Visible Wavelengths

During a solar eclipse, the moon blocks out the bright light of the body of the sun, making the wispy, outermost layer of the atmosphere, the corona, clearly visible. The corona is the hottest layer of the sun’s atmosphere, but the fundamental physics that govern the region are not well understood. A team, led by Philip Judge of the High Altitude Observatory in Boulder, Colorado, will use new instruments to study the magnetic field structure of the corona by imaging this atmospheric layer during the eclipse.

The instruments will observe the corona to see fingerprints left by the magnetic field in visible and near-infrared wavelengths from a mountaintop near Casper, Wyoming. The research will enhance our understanding of how the sun generates space weather, which can affect satellites in orbit around Earth. The instruments will simultaneously test new technology that can be compared to existing instrumentation, like NASA’s Hinode and Solar Dynamics Observatory, with the potential to be used in future missions. The results from this instrument will compliment data from an airborne study imaging the corona in the infrared, as well as another ground-based infrared study.

Measuring the Infrared Solar Corona

During the eclipse, a team of scientists led by Paul Bryans at the National Corporation for Atmospheric Research will sit inside a trailer in Camp Wyoba atop Casper Mountain in Wyoming, and point a specialized instrument at the sun. The instrument is a spectrometer, which collects light from the sun and separates each wavelength of light, measuring their intensity. This particular spectrometer, called the NCAR Airborne Interferometer, will for the first time survey infrared light emitted by the sun’s atmosphere, or corona. Such an experiment can only be conducted from the ground during an eclipse, when the sun’s bright face is blocked, revealing the much fainter corona.

This novel data will help scientists characterize the corona’s complex magnetic field — crucial information for understanding and eventually helping forecast space weather events. The scientists will augment their study by analyzing their results alongside corresponding space-based observations from other instruments aboard NASA’s Solar Dynamics Observatory and the joint NASA/JAXA Hinode.

Exploring the Physics of the Coronal Plasma through Imaging Spectroscopy

Shadia Habbal of the University of Hawaii’s Institute for Astronomy in Honolulu will lead a team of scientists to image the sun from four different states during the total solar eclipse. They will use spectrometers, which analyze the light emitted from different ionized elements in the corona. The scientists will also use unique filters to selectively image the corona in certain colors, which allows them to directly probe into the physics of the sun’s outer atmosphere. With this data, they can explore the composition and temperature of the corona, and measure the speed of particles flowing out from the sun. Different colors correspond to different elements — nickel, iron and argon — that have lost electrons, or been ionized, in the corona’s extreme heat, and each element ionizes at a specific temperature. By analyzing such information together, the scientists hope to better understand the processes that heat the corona — which is, counterintuitively, far hotter than the surface of the sun itself.

The team will operate from five different sites in four states: Mitchell, Oregon; Mackay, Idaho; Alliance, Nebraska; Guernsey, Wyoming; and Dubois, Wyoming. The sites are roughly 600 miles apart on the path of totality, which enables them to track short-term changes in the corona and also increases their chances for good weather conditions. This team has observed total eclipses before, however, they will add a new filter to their series this year.

Testing a Polarization Sensor for Measuring Temperature and Flow Speed in the Solar Corona

In Madras, Oregon, a team of NASA scientists led by Nat Gopalswamy at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, will point a new, specialized polarization camera at the sun’s faint outer atmosphere, the corona, taking several-second exposures of the sun at four selected wavelengths in just over two minutes. Their images will capture data on the temperature and speed of solar material in the corona. Currently these measurements can only be obtained from Earth-based observations during a total solar eclipse.

To study the corona at times and locations outside a total eclipse, scientists use instruments called coronagraphs, which mimic eclipses by using solid disks inside the instruments to block the sun’s bright face in a manner that approximates the function of the moon’s shadow. Typical coronagraphs use a polarizer filter in a mechanism that turns through three angles, one after the other, for each wavelength filter. The new camera is designed to eliminate this clunky, time-consuming, serial process, by incorporating thousands of tiny polarization filters to read light polarized in different directions simultaneously. Testing this instrument is a crucial step toward improving coronagraphs and ultimately, our understanding of the corona — the very root of the solar radiation that fills up Earth’s space environment.


Studying Earth’s Atmosphere

Solar Eclipse-Induced Changes in the Ionosphere Over the Continental US

The ionosphere, an electrically charged outer shell of Earth’s atmosphere, is affected by processes in deeper levels of the atmosphere, as well as by incoming sunlight and particles. Electrons and atoms in the region are constantly being shaken by travelling ionospheric disturbances, which move in ripples through the charged gas, ionized by the sun’s ultraviolet light. These disturbances in the ionosphere are often caused by a phenomenon known as atmospheric gravity waves, which can be triggered by eclipses. A team, led by Phil Erickson of MIT’s Haystack Observatory in Westford, Massachusetts, will use an extended network of sensors to monitor the ionosphere as it crosses America, in order to understand the large-scale effects of these disturbances.

Using over 6,000 ground-based sensors along with data from NASA’s space-based Thermosphere Ionosphere Mesosphere Energetics and Dynamics, or TIMED, mission, the team will monitor the changes in the ionosphere in real-time. The data will be publicly available during the eclipse and available online afterwards.

Land and Atmospheric Responses to the 2017 Total Solar Eclipse

Using an array of ground-based instruments and weather balloons, Bohumil Svoma, Jeffrey Wood and their team from the University of Missouri in Columbia, along with students and citizen scientists, will meticulously map the response of the land and lower atmosphere to the total solar eclipse. Measuring the temperature, humidity, winds, and carbon dioxide exchange throughout the Columbia, Missouri, area will give new insight into Earth’s response to eclipses. As the partial eclipse becomes total, the solar radiation in a given place will decrease more than three times faster than during a normal sunset, potentially prompting unique responses from plants and the local weather.

Quantifying the Contributions of Ionization Sources on the Ionosphere

The upper reaches of Earth’s atmosphere — a region ionized by solar and cosmic radiation — is a superhighway for long-range, very low frequency, or VLF, telecommunications transmissions. Known as the ionosphere, this layer of the atmosphere is used for sending VLF transmissions all around the world. A research project, led by Bob Marshall at the University of

Colorado Boulder, will use the unique conditions created by the eclipse to study the ionosphere in hopes of improving models of the region’s dynamics.

Radio wave transmissions sent from Lamoure, North Dakota, will be monitored at receiving stations across the eclipse path in Colorado and Utah. The data will be compared with several space-based missions, such as NOAA’s Geostationary Operational Environmental Satellite, NASA’s Solar Dynamics Observatory and NASA’s Ramaty High Energy Solar Spectroscopic Imager, to precisely characterize the effect of the sun’s radiation on the ionosphere.

Studying Earth’s Atmosphere During an Eclipse from Above and Below

During totality, the moon completely blocks direct solar radiation, dramatically decreasing the total amount of radiation that reaches the surface, as well as the radiation Earth’s atmosphere, clouds and oceans reflect back into space. These changes are represented by Earth’s ever- fluctuating radiation budget, the absolute irradiance the planet’s sunlit side experiences. Calculating this budget is a fundamental technique for accurately estimating atmospheric and surface temperatures during such fluctuations. A total solar eclipse presents a unique opportunity for investigating how the radiation budget changes. Guoyong Wen, an Earth scientist at NASA’s Goddard Space Flight Center, in Greenbelt, Maryland, leads a team to study these effects during the eclipse.

In Casper, Wyoming, the scientists will deploy two ground-based instruments: a spectrometer, which provides information on how much of any given wavelength of light is present, and a pyranometer, which measures total solar irradiance coming down toward the surface. Meanwhile, in space, the instruments EPIC and NISTAR aboard NASA’s DSCOVR will monitor Earth’s outgoing radiation. Additionally, NASA’s Terra satellite will provide observations of atmospheric and surface conditions.

The collection of data from both above and below forms what scientists call a 3-D closure experiment. The scientists plan to use this collection of data to build better radiation transfer models, and ultimately, improve our understanding of how Earth’s radiation budget changes.

Empirically-Guided Solar Eclipse Modeling of the Earth’s Ionosphere

The ionosphere — a region of Earth’s atmosphere made of charged particles — is a dynamic area, and one not fully understood. The total eclipse provides Greg Earle and his team at Virginia Tech in Blacksburg the opportunity to understand how the ionosphere responds to changes in sunlight. The team will use a network of radio transmitters and receivers across the country.

Earle and his team will be stationed across the United States in Bend, Oregon, Holton, Kansas, and at the Shaw Air Force Base in Sumter, South Carolina, using custom designed ionosodes, instruments that use radio waves to look up into the ionosphere and measure its height and density. Their measurements will be combined with data from a nation-wide network of GPS receivers and signals from the Ham Radio Reverse Beacon Network, both of which are sensitive to the state of the ionosphere. The team will also utilize data from Virginia Tech’s SuperDARN radars, two of which have been placed along the eclipse path in Christmas Valley, Oregon, and Hays, Kansas. By combining all the data, Earle and his team will be able to improve models of the ionosphere and understand what affect the eclipse had on the region.