Aurora borealis can sometimes produce spectacular explosions of light

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Washington, December 18 (ANI): A network of cameras deployed around the Arctic in support of NASA's THEMIS mission has discovered that sometimes, vast curtains of the aurora borealis collide, producing spectacular outbursts of light.

Movies of the phenomenon were unveiled at the Fall Meeting of the American Geophysical Union in San Francisco recently.

"Our jaws dropped when we saw the movies for the first time," said space scientist Larry Lyons of the University of California-Los Angeles (UCLA), a member of the team that made the discovery.

"These outbursts are telling us something very fundamental about the nature of auroras," he added.

The collisions occur on such a vast scale that isolated observers on Earth - with limited fields of view - had never noticed them before.

It took a network of sensitive cameras spread across thousands of miles to get the big picture.

THEMIS consists of five identical probes launched in 2006 to solve a long-standing mystery that why do auroras occasionally erupt in an explosion of light called a substorm.

Twenty all-sky imagers (ASIs) were deployed across the Alaskan and Canadian Arctic to photograph auroras from below while the spacecraft sampled charged particles and electromagnetic fields from above.

The breakthrough came earlier this year when UCLA researcher Toshi Nishimura assembled continent-wide movies from the individual ASI cameras.

The first movie Nishimura showed Lyons was a pair of auroras crashing together in December 2007.

"It was like nothing I had seen before. Over the next several days, we surveyed more events. Our excitement mounted as we became convinced that the collisions were happening over and over," Lyons recalled.

The explosions of light, according to the researchers, are a sign of something dramatic happening in the space around Earth-specifically, in Earth's "plasma tail," which is made of charged particles captured mainly from the solar wind.

According to THEMIS project scientist Dave Sibeck of NASA's Goddard Space Flight Center, Greenbelt, Maryland, "By putting together data from ground-based cameras, ground-based radar, and the THEMIS spacecraft, we now have a nearly complete picture of what causes explosive auroral substorms,"

Lyons and Nishimura have identified a common sequence of events.

It begins with a broad curtain of slow-moving auroras and a smaller knot of fast-moving auroras, initially far apart.

The slow curtain quietly hangs in place, almost immobile, when the speedy knot rushes in from the north.

The auroras collide and an eruption of light ensues. (ANI)

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