On 2 July, the shadow of the moon passed over South America, and the sun’s enigmatic outer layers became briefly visible. The total solar eclipse passed from the Pacific Ocean over Chile and Argentina before disappearing into the sunset.
Total eclipses occur when the moon is perfectly aligned to block out the entire disk of the sun during the day, which happens somewhere on Earth about once every 18 months. They present a unique opportunity to study the outer layer of the sun’s atmosphere, called the corona, which is not bright enough to see during the day.
Researchers have many questions about the corona that solar eclipses can help answer. For one, it is far hotter than the surface of the sun and we’re not sure why. It also has warmer and cooler patches that make the difference in temperature even harder to explain.
The corona is also where the consequences of magnetic activity within the sun are felt, in the form of huge bursts of plasma called coronal mass ejections. When these plasma plumes hit Earth, they can interfere with power grids and satellites, so they are important to predict, and understanding the corona’s magnetic field could help.
Astronomers were spread across the path of the total eclipse to catch a glimpse of the corona. This eclipse was harder to observe than the one that crossed the US in 2017 because most of it happened over the ocean and just before sunset, with the sun low in the sky. Nevertheless, solar astronomers hope it will be another step toward understanding the sun’s secrets.
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