A Total Solar Eclipse Revealed Solar Storms 100 Years Before Satellites
Just days from now, on Aug. 21, 2017, the Moon will pass between the Sun and Earth, casting its shadow down on Earth and giving all of North America the chance to see a solar eclipse. Remember that it is never safe to look at the partially eclipsed or uneclipsed Sun, so make sure you use a solar filter or indirect viewing method if you plan to watch the eclipse.
Eclipses set the stage for historic science. Past eclipses enabled scientists to study the Sun’s structure, find the first proof of Einstein’s theory of general relativity, and discover the element helium — 30 years before it was found on Earth..
We’re taking advantage of the Aug. 21 eclipse by funding 11 ground-based scientific studies. As our scientists prepare their experiments for next week, we’re looking back to an historic 1860 total solar eclipse, which many think gave humanity our first glimpse of solar storms — called coronal mass ejections — 100 years before scientists first understood what they were.
Coronal mass ejections, or CMEs, are massive eruptions made up of hot gas, plasma and magnetic fields. Bursting from the Sun’s surface, these giant clouds of solar material speed into space up to a million miles per hour and carry enough energy to power the world for 10,000 years if we could harness it. Sometimes, when they’re directed towards Earth, CMEs can affect Earth’s space environment, creating space weather: including triggering auroras, affecting satellites, and – in extreme cases – even straining power grids.
Scientists observed these eruptions in the 1970s during the beginning of the modern satellite era, when satellites in space were able to capture thousands of images of solar activity that had never been seen before.
But in hindsight, scientists realized their satellite images might not be the first record of these solar storms. Hand-drawn records of an 1860 total solar eclipse bore surprising resemblance to these groundbreaking satellite images.
On July 18, 1860, the Moon’s shadow swept across North America, Spain and North Africa. Because it passed over so much populated land, this eclipse was particularly well-observed, resulting in a wealth of scientific observations.
Drawings from across the path of the 1860 eclipse show large, white finger-like projections in the Sun’s atmosphere—called the corona—as well as a distinctive, bubble-shaped structure. But the observations weren’t uniform – only about two-thirds of the 1860 eclipse sketches showed this bubble, setting off heated debate about what this feature could have been.
Sketches from the total solar eclipse of July 1860.
One hundred years later, with the onset of space-based satellite imagery, scientists got another piece of the puzzle. Those illustrations from the 1860 eclipse looked very similar to satellite imagery showing CMEs – meaning 1860 may have been humanity’s first glimpse at these solar storms, even though we didn’t understand what we were seeing.
While satellites provide most of the data for CME research, total solar eclipses seen from the ground still play an important role in understanding our star. During an eclipse, observers on the ground are treated to unique views of the innermost corona, the region of the solar atmosphere that triggers CMEs.
This region of the Sun’s atmosphere can’t be measured at any other time, since human-made instruments that create artificial eclipses must block out much of the Sun’s atmosphere—as well as its bright face—in order to produce clear images. Yet scientists think this important region is responsible for accelerating CMEs, as well as heating the entire corona to extraordinarily high temperatures.
When the path of an eclipse falls on land, scientists take advantage of these rare chances to collect unique data. With each new total solar eclipse, there’s the possibility of new information and research—and maybe, the chance to reveal something as astronomical as the first solar storm.
Learn all about the Aug. 21 eclipse at eclipse2017.nasa.gov, and follow @NASASun on Twitter and NASA Sun Science on Facebook for more. Watch the eclipse through the eyes of NASA at nasa.gov/eclipselive starting at 12 PM ET on Aug. 21.
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