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When the moon passes in front of the sun on August 21 for the historic total solar eclipse, day will briefly become night, before returning to brightness moments later.

According to NASA, this will effectively turn off the source of high-energy radiation in the ionosphere, a layer that extends from about 50 to 400 miles above Earth's surface.

The ionosphere is constantly changing in response to the sun's activity, and the upcoming eclipse will give scientists an unprecedented opportunity to study the mechanisms behind these changes.

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 The August 21 eclipse will effectively turn off the source of high-energy radiation in the ionosphere, a layer that extends from about 50 to 400 miles above Earth's surface. The path of the eclipse, and the moon's shadow, is shown above. The varying colors illustrate how it will affect insolation

The ionosphere is an electrified layer of Earth's atmosphere, NASA explains.

It's in constant flux, growing and shrinking based on solar activity and space weather.

This, in turn, can cause disruptions to communication and navigation signals.

The three research teams backed by NASA will investigate this layer to find out more about the sun's role in its behaviour.

'The eclipse turns off the ionosphere's source of high-energy radiation,' said Bob Marshall, a space scientist at University of Colorado Boulder and principal investigator for one of the studies.

'Without ionizing radiation, the ionosphere will relax, going from daytime conditions to night-time conditions and then back again after the eclipse.'

The eclipse will see the sun briefly covered by the moon, blocking the radiation from hitting the ionosphere.

During this time, the researchers will be able to determine just how much radiation has been blocked, along with the area this extends to, and for how long.

'In our lifetime, this is the best eclipse to see,' said Greg Earle, an electrical and computer engineer at Virginia Tech in Blacksburg, Virginia, who is leading another of the studies.

'But we've also got a denser network of satellites, GPS and radio traffic than ever before.

'It's the first time we'll have such a wealth of information to study the effects of this eclipse; we'll be drowning in data.'

The team will use automated communication or navigation signals to track the ionosphere's behaviour.

In a normal night-day cycle, the concentration of charged atmospheric particles waxes and wanes with the sun, according to NASA.

According to NASA, the ionosphere is split into three distinct regions based on what wavelength of solar radiation is absorbed. These are the D, E and F, with D being the lowermost region and F, the uppermost

The ionosphere is an electrified layer of Earth's atmosphere, NASA explains . It's in constant flux, growing and shrinking based on solar activity and space weather. This, in turn, can cause disruptions to communication and navigation signals

The new measurements will provide new insight on solar input and the ionospheric response, in a step toward better understanding these interactions.

'Compared to visible light, the Sun's extreme ultraviolet output is highly variable,' said Phil Erickson, a principal investigator of a third study and space scientist at Massachusetts Institute of Technology's Haystack Observatory.

'That creates variability in ionospheric weather. Because our planet has a strong magnetic field, charged particles are also affected along magnetic field lines all over the planet – all of this means the ionosphere is complicated.'

'In the daytime, ionospheric plasma is dense,' Earle said.

'When the sun sets, production goes away, charged particles recombine gradually through the night and density drops.

'During the eclipse, we're expecting that process in a much shorter interval.'

When the concentration of the charged particles, called plasma, is denser, the signals are more likely to bump into them as they pass from the transmitter to the receiver.

This will alter the path of the signals themselves.

During the eclipse, the experts expect the signals will be stronger, as the atmosphere and ionosphere will absorb less transmitted energy.

'If we set up a receiver somewhere, measurements at that location provide information on the part of the ionosphere between the transmitter and receiver,' Marshall said.

PROTECTING YOUR EYES

Viewers must also be prepared with the proper gear to protect their eyes during the event. Otherwise, NASA warns, you could 'severely hurt your eyes'

The space agency says viewers should be equipped with special specs such as Rainbow Symphony, American Paper Optics, Thousand Oaks Optical, and TSE 17.

These are just four that meet the ISO 12312-2 international standard.

And, they warn that you should never look at the sun through an unfiltered camera, telescope, binoculars.

According to NASA, eclipse glasses should be put on when the partial eclipse begins, meaning when the sun becomes partially covered by the moon.

And, they should remain on for the entirety of the phases leading up to totality.

Once the moon has completely blocked out the sun, causing it to suddenly become dark, viewers can then remove the glasses for a short amount of time.

This may last just a minute, though, and the glasses will need to be put back on for the final stages of the eclipse.

'We use the receivers to monitor the phase and amplitude of the signal. When the signal wiggles up and down, that's entirely produced by changes in the ionosphere.'

The researchers will transmit electromagnetic signals back and forth along the path of totality, which stretches from the coast of Oregon to the coast of South Carolina.

Doing this, they'll be able to collect data before and after the eclipse, to compare the eclipse response to the baseline.

According to NASA, the ionosphere is split into three distinct regions based on what wavelength of solar radiation is absorbed.

When the moon passes in front of the sun on August 21 for the historic total solar eclipse, day will briefly become night, before returning to brightness moments later

These are the D, E and F, with D being the lowermost region and F, the uppermost.

And, the researchers will be studying all of them.

'Just because the density is low, doesn't mean it's unimportant,' Marshall said.

'The D-region has implications for communications systems actively used by many military, naval and engineering operations.'  

'We may even see global-scale effects,' Erickson said. 'Earth's magnetic field is like a wire that connects two different hemispheres together. Whenever electrical variations happen in one hemisphere, they show up in the other.'

Earle's team will be positioned across the country, in Bend, Oregon; Holton, Kansas; and Shaw Air Force Base in Sumter, South Carolina.

The researchers will measure the ionosphere's height and density using instruments called ionosondes.

They'll also combine their measurements with data from a nation-wide GPS network, as well as signals from the ham radio Reverse Beacon Network.

'We're looking at the bottom side of the F-region, and how it changes during the eclipse,' Earle said. 'This is the part of the ionosphere where changes in signal propagation are strong.'

The work could help pave the way for mitigation methods to fight radio signal disturbances, according to NASA.

And, it could lead to better understanding of the ionosphere.

'Others have studied eclipses throughout the years, but with more instrumentation, we keep getting better at our ability to measure the ionosphere,' Erickson said. 'It usually uncovers questions we never thought to ask.'