10:00 AM | *The next “Great American” total solar eclipse is less than two years away…timing of the current solar cycle may be just right for studying the corona*
Paul Dorian
In case you missed the last “Great American total solar eclipse”, the next one in the US is 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)
Overview
It was almost five years 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 to study the sun’s outer atmosphere known as the corona. What was referred to as “The Great American Solar Eclipse” took place on August 21st, 2017 when the moon passed between the sun and earth. The result was a 67-mile wide shadow that crossed the country all the way from Oregon-to-South Carolina. In case you missed the August 2017 total solar eclipse or it turned out to be cloudy in your given area, there will be another chance in the not-too-distant future coming on Monday, April 8th, 2024.
The chart above lists the moment when the eclipse and totality begin and end for a handful of locations that lie within the totality path. (Info courtesy NASA)
Discussion
On average, two to five solar eclipses occur each year, but these don't always result in total eclipses. For example, there will be a solar eclipse that will cross the continental U.S. on Oct. 14, 2023 and it will be annular, meaning the moon will block only the center of the sun, leaving an outer ring of the solar disk visible. Total solar eclipses occur somewhere on Earth every year or so, but generally cast their shadows over oceans or remote land masses. 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 the last total solar eclipse in this country 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. The “totality zone” of the April 2024 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 the second time during these two celestial events.
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.
Great opportunity to study the corona
Total solar eclipses provide rare opportunities to gather information for many scientific disciplines including solar dynamics, heliophysics and atmospheric science. As an example, these events are great for studying the sun’s wispy outer atmosphere known as the corona as the brightness of the sun typically drowns out this outer layer. Indeed, 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 gather useful data during total solar eclipses with the next opportunity here coming in 2024.
Numerous sunspots are visible today as solar cycle 25 ramps up in activity. This current cycle began in late 2020 and could reach a maximum during 2024. Image courtesy spaceweather.com, NASA
The current solar cycle, #25, began in late 2020 and it is on an upswing in activity with several sunspots visible at this time. The expected solar maximum phase of cycle 25 may actually turn out to be very advantageous for scientists to study the corona during the April 2024 eclipse. Current trends point to the sun having about 125 sunspots when it peaks and this may just occur right around springtime of 2024. A more active sun usually is correlated with a more dynamic corona which is making for a lot of excitement in the solar scientist community regarding the April 2024 total solar eclipse. Solar cycle 24 peaked with about 115 sunspots visible at the peak which was much lower than the 180 of the prior cycle #23.
One of the findings during the 2017 total solar eclipse regarding the corona was that there were 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.
If you miss this next one you may regret it
The next total solar eclipse visible from the U.S. after the 2024 eclipse will occur in 2044. This eclipse will be visible in Montana, the Prairie Provinces of Canada and the Arctic. The next “cross-continental” total eclipse will happen the following year, in 2045, when the moon's shadow will sweep across the U.S. from northern California down to Florida.
Get ready…the next “Great American Solar Eclipse” is fast approaching.
Meteorologist Paul Dorian
Arcfield
arcfieldweather.com
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