Most logical explanation to me was the “exploding meteorite” theory except the flash duration and color are seemingly consistent. However from my research into this topic, I understand it is quite rare to observe exploding meteorites. I have observed the flashes hours into the night, much after sunset, so I ruled out sunset “green flash”. So consistent are the flash color and duration that they seem manmade to me. Which got me wondering, (background is aerospace and mechanical engineering) if this could be related to some sort of classified military tech. Theorize that if there is a sufficiently bright light source high enough above the atmosphere to scatter, it could be a form of radar used to periodically scan for incoming enemy missiles, stealth aircraft… potential detection by looking upwards for an object’s shadow. Sounds crazy I know…
Other than that I cannot rule out atmospheric electrical discharges absent of any cloud cover. Not sure if such a meteorological phenomenon exists or not. But they do look a LOT like when distant flashes of lightning illuminate the sky.