Late on Tuesday afternoon, the moon blocked the sun in South America.

Millions of people living in cities from La Serena, Chile, to San Juan, Argentina, were witness the event as shadows spread over hills and an uncanny coolness invades deserts. Many more have ventured to the region specifically for the spectacle — one that some astronomers called the Great South American Eclipse.

The celestial phenomenon was the first total solar eclipse since August 2017, generating excitement among professional astronomers, eclipse chasers and casual observers because it offered the opportunity to see pale tendrils of the sun’s atmosphere, or corona.

“We only get a few minutes to see the solar corona during an eclipse,” said Ivo Saviane, an astronomer at the La Silla Observatory situated on the outskirts of the Chilean Atacama Desert. “But this is a great chance to see the corona shoot ultrahot gas and study mechanisms like solar wind, which are still quite mysterious,” he said.[See photos from Tuesday’s solar eclipse.]

It started above the southern Pacific Ocean at 12:55 p.m. Eastern time and then arced toward the western coast of Chile. As the moon bit into more of the sun, daylight slowly became dimmer.