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What Scientists Are Learning from the Eclipse

While millions of people in North America headed outside to watch the eclipse on Aug. 21, 2017, hundreds of scientists got out telescopes, set up instruments, and prepared balloon launches – all so they could study the Sun and its complicated influence on Earth.

Total solar eclipses happen about once every 18 months somewhere in the world, but the August eclipse was rare because of its long path over land. The total eclipse lasted more than 90 minutes over land, from when it first reached Oregon to when it left the U.S. in South Carolina.

This meant that scientists could collect more data from land than during most eclipses, giving us new insight into our world and the star that powers it.

A moment in the Sun’s atmosphere

During a total solar eclipse, the Sun’s outer atmosphere, the corona, is visible from Earth. It’s normally too dim to see next to the Sun’s bright face, but, during an eclipse, the Moon blocks out the Sun, revealing the corona.

Image Credit: Peter Aniol, Miloslav Druckmüller and Shadia Habbal

Though we can study parts of the corona with instruments that create artificial eclipses, some of the innermost regions of the corona are only visible during total solar eclipses. Solar scientists think this part of the corona may hold the secrets to some of our most fundamental questions about the Sun: Like how the solar wind – the constant flow of magnetized material that streams out from the Sun and fills the solar system – is accelerated, and why the corona is so much hotter than the Sun’s surface below.  

Depending on where you were, someone watching the total solar eclipse on Aug. 21 might have been able to see the Moon completely obscuring the Sun for up to two minutes and 42 seconds. One scientist wanted to stretch that even further – so he used a pair of our WB-57 jets to chase the path of the Moon’s shadow, giving their telescopes an uninterrupted view of the solar corona for just over seven and half minutes.

These telescopes were originally designed to help monitor space shuttle launches, and the eclipse campaign was their first airborne astronomy project!

These scientists weren’t the only ones who had the idea to stretch out their view of the eclipse: The Citizen CATE project (short for Continental-America Telescopic Eclipse) did something similar, but with the help of hundreds of citizen scientists. 

Citizen CATE included 68 identical small telescopes spread out across the path of totality, operated by citizen and student scientists. As the Moon’s shadow left one telescope, it reached the next one in the lineup, giving scientists a longer look at the way the corona changes throughout the eclipse.

After accounting for clouds, Citizen CATE telescopes were able to collect 82 minutes of images, out of the 93 total minutes that the eclipse was over the US. Their images will help scientists study the dynamics of the inner corona, including fast solar wind flows near the Sun’s north and south poles.

The magnetized solar wind can interact with Earth’s magnetic field, causing auroras, interfering with satellites, and – in extreme cases – even straining our power systems, and all these measurements will help us better understand how the Sun sends this material speeding out into space.

Exploring the Sun-Earth connection

Scientists also used the eclipse as a natural laboratory to explore the Sun’s complicated influence on Earth.

High in Earth’s upper atmosphere, above the ozone layer, the Sun’s intense radiation creates a layer of electrified particles called the ionosphere. This region of the atmosphere reacts to changes from both Earth below and space above. Such changes in the lower atmosphere or space weather can manifest as disruptions in the ionosphere that can interfere with communication and navigation signals.

One group of scientists used the eclipse to test computer models of the ionosphere’s effects on these communications signals. They predicted that radio signals would travel farther during the eclipse because of a drop in the number of energized particles. Their eclipse day data – collected by scientists spread out across the US and by thousands of amateur radio operators – proved that prediction right.

In another experiment, scientists used the Eclipse Ballooning Project to investigate the eclipse’s effects lower in the atmosphere. The project incorporated weather balloon flights from a dozen locations to form a picture of how Earth’s lower atmosphere – the part we interact with and which directly affects our weather – reacted to the eclipse. They found that the planetary boundary layer, the lowest part of Earth’s atmosphere, actually moved closer to Earth during the eclipse, dropped down nearly to its nighttime altitude.

A handful of these balloons also flew cards containing harmless bacteria to explore the potential for contamination of other planets with Earth-born life. Earth’s stratosphere is similar to the surface of Mars, except in one main way: the amount of sunlight. But during the eclipse, the level of sunlight dropped to something closer to what you’d expect to see on Mars, making this the perfect testbed to explore whether Earth microbes could hitch a ride to the Red Planet and survive. Scientists are working through the data collected, hoping to build up better information to help robotic and human explorers alike avoid carrying bacterial hitchhikers to Mars.

Image: The small metal card used to transport bacteria.

Finally, our EPIC instrument aboard NOAA’s DSCOVR satellite provided awe-inspiring views of the eclipse, but it’s also helping scientists understand Earth’s energy balance. Earth’s energy system is in a constant dance to maintain a balance between incoming radiation from the Sun and outgoing radiation from Earth to space, which scientists call the Earth’s energy budget. The role of clouds, both thick and thin, is important in their effect on energy balance.

Like a giant cloud, the Moon during the total solar eclipse cast a large shadow across a swath of the United States. Scientists know the dimensions and light-blocking properties of the Moon, so they used ground- and space-based instruments to learn how this large shadow affects the amount of sunlight reaching Earth’s surface, especially around the edges of the shadow. Measurements from EPIC show a 10% drop in light reflected from Earth during the eclipse (compared to about 1% on a normal day). That number will help scientists model how clouds radiate the Sun’s energy – which drives our planet’s ocean currents, seasons, weather and climate – away from our planet.

For even more eclipse science updates, stay tuned to nasa.gov/eclipse.

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