8:00 AM | *Almost a year has passed since the “Great American Solar Eclipse” and there are some important preliminary findings…another opportunity comes in 2024*

In a composite photo, the International Space Station passes in front of the sun during the total eclipse on August 21, 2017. Credit: NASA

Overview
It was just about one year ago when America went crazy for the first coast-to-coast total solar eclipse on US soil since 1918 and it provided a great opportunity for scientists.  Next week marks the one-year anniversary of what was referred to as “The Great American Solar Eclipse” as on August 21st, 2017, the moon passed between the sun and earth and the result was a 67-mile wide shadow that crossed the country from Oregon-to-South Carolina.  Total solar eclipses occur somewhere on Earth every year or so, but generally cast their shadows over oceans or remote land masses.  If you missed last year’s total solar eclipse or it turned out to be cloudy in your area then there will be another opportunity in the not-too-distant future during April 2024.  
 

Image of the sun near totality, credit NASA

Recap of the “Great American Solar Eclipse” in August 2017
The previous total solar eclipse in the contiguous United States before last year took place in early 1979 and it only clipped the northwestern part of the country.  On that particular day, Feb. 26, 1979, it was cold and dreary in the Pacific Northwest, and most people in the path of totality actually could not even view the eclipse due to clouds and rain.  On August 21, 2017, generally favorable sky conditions across the country permitted millions of Americans to witness the total solar eclipse when the moon moved in between the earth and the sun and cast a shadow over much of the nation.
 

On August 21, 2017, the moon passed between earth and the sun in a total solar eclipse that was visible on a path from Oregon-to-South Carolina. Map courtesy NASA

The 67-mile wide path of the moon’s umbral shadow during last year’s total solar eclipse began in the northern Pacific and crossed the U.S. from northwest-to-southeast through parts of the following states: Oregon, Idaho, Montana, Wyoming, Nebraska, Kansas, Missouri, Illinois, Kentucky, Tennessee, North Carolina, Georgia, and South Carolina. It passed directly over such cities as Salem, Oregon, Idaho Falls, Idaho, Lincoln, Nebraska, Kansas City, Missouri, Nashville, Tennessee and Charleston, South Carolina.  At any given location along the “totality path”, the eclipse lasted for around 2 or 3 minutes turning day into a dark twilight.  Some stars even became visible during the event which lasted in its entirety for about three hours from start to finish. 

The sun's tenuous outer atmosphere is called the corona and it becomes visible during a total solar eclipse. The corona is not normally visible since the sun's disk is so bright that the relatively faint light from the wispy corona is simply overwhelmed.

Some important preliminary findings
The total solar eclipse of 2017 provided a rare opportunity to gather information for many scientific disciplines including solar dynamics, heliophysics and atmospheric science.  For example, this was a great chance to study the sun’s wispy outer atmosphere called the corona as its overwhelming brightness usually drowns out the faint corona and not even a 99 percent eclipse will reveal the sun’s corona.  Temperatures in the corona can reach 1 million°C, making the region much hotter than the solar surface, which is “just” 6,000°C or so. How the corona gets so hot has puzzled scientists for decades and solar scientists gathered useful data during the total solar eclipse which is still being analyzed today.  

In one project, the National Solar Observatory deployed 68 small telescopes to amateur astronomers across the path of the eclipse so that at all times at least one telescope was in the shadow looking at the sun’s corona.  This resulted in a ton of data with more than 45,000 images and plenty left to analyze in months and years to come.  One of the early findings was somewhat of a surprise as there are indications of a more complex interaction than previously thought between the “cold” lower atmosphere of the sun known as the chromosphere and the hot outer atmosphere layer (corona).  A relatively narrow area called the transition region separates the corona from the chromosphere. Temperatures rise sharply in the transition region, from thousands of degrees in the chromosphere to more than a million degrees in the corona. The density of plasma falls rapidly through the transition region moving upward from the chromosphere to the corona.

Another area of particular interest to atmospheric scientists was how the total solar eclipse would affect the ionosphere which is the barrier region between the atmosphere and what we think of as outer space.  It is in the ionosphere where auroras occur and where the International Space Station and low Earth orbit satellites are found.  The ionosphere is affected by radiation from the sun above and by weather systems below. The eclipse gave researchers the chance to study what happens to the ionosphere when solar radiation drops suddenly, as opposed to the gradual changes of the day-night cycle.  In essence, a total solar eclipse essentially creates a “hole” in the ionosphere and most models predicted beforehand that this would allow radio waves to travel much farther and faster than usual. As it turns out, preliminary findings from the 2017 total solar eclipse suggest the models are correct in their predictions.

In many regions, scientists meticulously mapped responses by the atmosphere to the total eclipse by measuring ambient temperature, humidity, winds and changes in carbon dioxide. There were several teams that launched numerous weather balloons to take measurements from the surface to way up in the atmosphere around 100,000 feet high. This data is still under analysis and results are sure to come in the near future.

In case you missed the last total solar eclipse, the next one in the US is actually not that far away coming on April 8th, 2024.  Here are the “totality zone” tracks for the 2017 and 2024 solar eclipses (map courtesy eclipse-maps.com)

Next chance in April 8th, 2024
In case you missed the August 2017 total solar eclipse or it turned out to be cloudy in your area, there will be another chance in the not-too-distant future coming on Monday, April 8th, 2024.  The “totality zone” of this event will extend on a southwest-to-northeast path from Texas-to-Maine.  And if you happen to live in southern Illinois or southeastern Missouri then you will be lucky enough to be in the “totality zone” for a second time during the upcoming April 2024 event.

Meteorologist Paul Dorian
Perspecta, Inc.
perspectaweather.com 

Detailed video discussion on the “Great American Solar Eclipse” of August 2017: