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Practicing science in the dark

Speed read
  • Solar eclipses have led to some of the greatest discoveries in human history
  • Coronal magnetic field plays a big role in space weather
  • Next total solar eclipse to cross the US comes in 2024

On August 7, 1869, Theophilus Adam Wylie and his colleagues at Indiana University climbed to the roof of the Wylie House on campus to view a rare event: A full solar eclipse.

Afterwards, Wylie wrote in his journal: “Witnessed the total eclipse of the sun. A most magnificent sight. The coronas blended, extending on average about a quarter diameter of the moon’s disc all around. Noticed a bat flying around. The whole landscape had an unearthly, unnatural respect.”

<strong>Hot Stuff. </strong> This eruptive prominence lifted off from the sun on Sept. 15, 2010 and shows off the strands of plasma in exquisite detail. Prominences are cooler clouds of gases suspended above the sun by often unstable magnetic forces. Courtesy NASA; Solar Dynamics Observatory.

Since then, the way astronomers work has changed. It might’ve been difficult for Wylie to imagine doing a quadrillion calculations for chemistry research in less than five seconds on the Little Green Machine II supercomputer, for example.

But one thing is the same: Solar eclipses are still a great opportunity for researchers to collect data and make observations about the natural world.  

A cosmic mystery

As Wylie writes in his journal, eclipses are a golden opportunity to study the sun’s corona. Without special equipment, it is virtually invisible during the daytime.  

Many observatories on the ground, such as the Big Bear Solar Observatory in California, monitor various layers of the sun’s atmosphere. The corona is the outermost layer, stretching thousands of miles above the sun’s surface.

<strong>Laws of attraction. </strong> Knowledge of the solar magnetic field is essential for space weather prediction. This image shows the expected direction of the coronal magnetic field during the total solar eclipse on August 21, 2017. Courtesy NCAR; HAO; Predictive Science Inc.

During an eclipse, researchers can explore how the corona works, such as how sun’s energy gets transported into the corona.

The surface of the sun has a temperature of roughly 10,000º Fahrenheit. The thin gas that makes up the corona far above the sun, however, has a much hotter temperature, nearing millions of degrees Fahrenheit on average.

That transport process remains a mystery to scientists.

It’s magnetic

Another focal point for scientists during the eclipse is the corona’s unique magnetic fields.

The magnetic fields cause solar flares, which are powerful emissions of pent-up radioactive energy on the sun’s surface.

These flares take roughly eight minutes to reach earth. Tracking them is important because they can disrupt communications satellites that rely on radio waves, affecting life on our blue marble.

The High Altitude Observatory (HAO) at the National Center for Atmospheric Research (NCAR) plans on measuring these magnetic fields during the eclipse with a tool known as a Fourier transform spectrometer (FTS), originally created to collect data about earth’s troposphere and stratosphere.

The FTS uses an algorithm to transform the raw light data collected by its mirrors into an analysis of the intensities of individual wavelengths.<strong>Birds of a feather. </strong> Albert Einstein and Sir Arthur Eddington chatting about genius stuff. Eddington's documentation of star positions before and after a solar eclipse demonstrated Einstein's theory of general relativity to be correct. Courtesy Royal Observatory Greenwich.

For this year’s total eclipse, the FTS will be installed in remote Wyoming to target infrared emissions from the sun that are sensitive to the sun’s magnetic fields, providing information about the fields and the corona’s wavelength range.

A special opportunity

The last time a solar eclipse’s path of totality crossed the continental United States was 99 years ago on June 8, 1918.

Scientists hoped they could track the eclipse to confirm Einstein’s general theory of relativity, but cloud cover obscured the eclipse for most potential viewers in the United States, leaving Einstein’s theory unconfirmed until the next total solar eclipse in 1919.

With clear skies forecasted for plenty of areas in middle America, however, most sky watchers will have the chance to take in some of the same unnatural effects Wiley observed 148 years ago.

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