When mysterious glowing stripes of green lit up Finnish skies in 2018, it didn’t go unnoticed by avid aurora chasers. The pattern of light was unfamiliar and strangely perfect, reaching out toward the horizon like a set of celestial sand dunes.

Sure enough, the light show dubbed by the citizen scientists as “the dunes” turned out to be a new type of aurora. This aurora is formed by the dramatic dance of gravity waves and oxygen atoms, according to new findings published today (Jan. 29) in the journal AGU Advances.