Satellites, airplanes, and balloons can have flashing lights on them to indicate position, but they can also reflect light from way beyond the horizon, resulting in seemingly impossibly bright flashes. The Iridium satellites used to do this reliably and often before they were deorbited, but now OneWeb and Starlink have taken up that mantle with far greater prevalence and annoyancem

Space debris can do this too, like failed Iridium satellites, ALOS, or rocket bodies tumble throughspace and their flares are basically unpredictable.