'What's creating these long glowing streaks in the sky? No one is sure’

This stunning image shows a celestial phenomenon called “STEVE” which has been baffling NASA scientists for years.

The dazzling light display was first reported in 2015, but space experts are still struggling to understand what exactly it is.

It consists of a “purple ribbon in the sky, with a green picket fence structure underneath”, according to NASA, which named it “Strong Thermal Emission Velocity Enhancement” – or STEVE for short.

The agency describes it as “aurora-like”, meaning it is similar to the natural electric phenomenon that causes the Northern Lights.

One thing researchers do know is that STEVE is not a normal aurora. It may not be an aurora at all, according to some.

“I’m not entirely sure about anything with respect to this phenomenon just yet,” said Boston University professor Joshua Semeter – one of the researchers on a paper about the mysterious feature.

STEVE’s purple emissions are likely a result of ions moving at “supersonic speed”, NASA said on its website last week.

“The green emissions seem to be related to eddies, like the ones you might see forming in a river, moving more slowly than the other water around it,” it added.

To identify STEVE’s features, researchers have extensively used photos and videos captured by so-called citizen scientists.

“Citizen scientists are the ones who brought the STEVE phenomenon to the scientists’ attention,”  Elizabeth MacDonald, a space scientist at NASA’s Goddard Space Flight Center in Maryland, explained.

“Their photos are typically longer time lapse than our traditional scientific observations.”

Photographer Neil Zeller said he had not originally planned to be a citizen scientist. “It was just for the beauty of it,” he admitted.

But Mr Zeller has been involved with the discovery of STEVE from the start, NASA said.

It was thanks to a photo he took of the phenomenon years ago, which he then showed to Ms MacDonald, that research into STEVE was launched. Now he is a co-author on NASA’s research paper.

“It’s an honor, it really is,” Mr Zeller said about contributing to the study.

“I tend to take a step back from the scientists doing the work. I’m out there for the beauty of it and to capture these phenomena in the sky.”