Swamp gas can sometimes appear to glow when the light from Venus strikes from behind. This illusion is what's behind most sightings of weather balloons.
I may be remembering wrong but I think these were from when air force pilots came across something they had no idea what it was and it was faster than them. Thing is these were leaked a long time ago but relatively recently they were confirmed real footage or something like that.
Could be wrong but that's how I remember it being explained
Could be wrong but that's how I remember it being explained