The corona is the outermost part of the Sun’s atmosphere that Earth’s inhabitants can only see during a total solar eclipse. Its appearance is constantly evolving due to the sun’s ever-changing magnetic field and is different during each solar eclipse. But April 8 will be especially stunning, according to a recently released simulation from Predictive Science, a San Diego-based company that develops computer models of the sun and whose work supports a number of NASA missions.
The simulation reveals a dramatic starburst-like pattern with multiple large bulges, including at 7 o’clock, 10 o’clock, and 2 o’clock. Closer to the solar disk, several contour features are also visible.
Predictive Science has a history of successful eclipse predictions. But this eclipse will be harder to predict than normal. This is because the current 11-year solar cycle is near its peak, or maximum, when the sun’s magnetic field is at its most chaotic.
The behavior of this magnetic field is important because it distorts the plasma, or glowing superheated gas, that makes up the corona. This glowing plasma tracks the sun’s magnetic field.
“The magnetic flux on the sun near solar maximum changes a lot,” John Linker, president of Predictive Science, said in an interview. “We used to be able to do a month in advance [prediction] and then another forecast a week in advance. But right now the sun is very dynamic, which makes it very challenging. This year we’re doing something more ambitious as it’s a model that evolves over time.”
Despite the challenges in forecasting, Bob Leaman, a NASA researcher focused on solar physics, said he expects it to be the most spectacular corona in existence.
During eclipses, the corona tends to be least interesting during solar minimum, when the sun may remain without sunspots for days or weeks. Sunspots are regions of increased magnetism on the sun; the absence of sunspots means an undetectable magnetic field and a fairly simple corona. At the sun’s north and south poles, “polar jets” of plasma follow the magnetic field lines from or into the sun, but there aren’t many contours, bulges, or notable features.
This was the case in 2019 during a total eclipse in Chile:
But with solar maximum slated for sometime in mid-2024, scientists expect the most dynamic corona possible.
“The greater the solar activity, the more spikes are around from the sun,” Leamon said. “I think it’s going to be really cool.”
On April 20 last year a brief total solar eclipse gave a 1 minute 2 second total blackout to areas near Learmonth on the most north-western cape of Australia. Notice how much more dynamic the corona was compared to the 2019 eclipse:
There are even more reasons why the April 8 crown has the potential to be quite special. Two large sunspot clusters could distort the corona into even more spectacular shapes.
Of particular interest is the rebirth of AR3590 (AR stands for Active Region), a sunspot cluster that produced a trio of top-class X-class flares in late February. It can spin from the far side of the sun back into view, which can produce bulges or large bands and loops of magnetism.
Besides bulges, there’s a chance we’ll catch a glimpse of a dramatic solar phenomenon known as a coronal mass ejection, or CME. It is an eruptive burst of plasma and magnetism from a sunspot. CMEs can interact with Earth’s magnetic field and produce auroras for our viewing pleasure (but they usually take at least a day or two before bombarding our magnetic field).
“With flares and flares, there’s a very real possibility that we’ll see a CME come out on the side of the sun,” Leamon said. “That would be absolutely awesome.”
During the eclipse, ground-based observers will only see a CME phase within a few minutes, such as the ejection of some material from the sun. The entire eruption will last an hour or more, which can be observed by stitching together multiple images taken by humans or scientific instruments along the path of totality.
“You can see a big bubble coming out of the sun,” Linker said. “I think even in the last few eclipses there were small CMEs and there are drawings in the past where people would sketch that bubble.” Some of those drawings date back to the 1870s.
If one starts just before the aggregate, he hopes that his time-evolving model will catch it and predict its behavior – and what it will look like.
Predictive Science plans to continually update its corona predictions as more data becomes available leading up to the eclipse. They can be accessed here.