The aurora borealis are gorgeous displays of light that fascinate and mesmerize people the world over. They are also known as the Northern Lights in the Northern hemisphere, and the Southern Lights in the Southern hemisphere. The Sun can release charged particles into space, some of which may be directed at Earth. While the Earth's magnetic fields deflect most of these particles, some interact with the atmosphere, generating these dazzling light displays in the process.
Many colors can be seen in auroras, which depend on which molecules are hit by the Sun's particles. Green, for example, is generated when charged particles hit oxygen that is sitting from 100 to 200 kilometers over the ground. Nitrogen produces different colors, including pink, purple, and blue hues.
White light in auroras has also been documented anecdotally and in some old scientific publications. Now, scientists have found an explanation for the white patches that are sometimes visible along with the Northern lights. They are generated by ahat is called a "structured continuum emission" that is linked to the aurora. The findings have been reported in Nature Communications.
"You'd see this dynamic green aurora, you'd see some of the red aurora in the background and, all of a sudden, you'd see this structured, almost like a patch, grey-toned or white toned-emission connected to the aurora," explained first study author Dr. Emma Spanswick, PhD, an associate professor at the University of Calgary. "So, the first response of any scientist is, 'Well, what is that?'"
This study has determined that the white patch is likely some kind of heat source, which also suggests that the aurora phenomenon may be more complex than we know.
Researchers have been able to clearly identify and explain these white aurora patches because photographic technology has advanced so much that we are now able to see true colors in images of the night sky.
"Everyone has noticed the advancement in digital photography. Your cellphone can now take pictures of the aurora," said Spanswick. "That has flowed to the commercial sensor market now. Those types of sensors can now be found in more commercial, more robust sensors that we would use in science."
Spanswick added that this light also has some similarities to another light phenomenon known as STEVE (Strong Thermal Emission Velocity Enhancement), a bright ribbon of mauve or grey light in the sky.
"To be honest, the elevation of the spectrum between the two is very similar but this, because of its association with dynamic aurora, it's almost embedded in the aurora. It's harder to pick out if you were to look at it, whereas STEVE is separate from the aurora: a big band crossing the sky."
Sources: University of Calgary, Nature Communications
