I remember once when I was a kid in Honolulu, looking up into the night sky and seeing an eerie green trail. Turns out the military launch facility on Kauai (Barking Sands) was launching a series of barium/copper payloads on sounding rockets into the upper atmosphere. Barium, like cesium is a highly reactive element and when the payload ionized it turned green. We never get to see the Northern Lights this far south, so it was a terrific light show.