Another source of bright drifting objects, Iridium communication satellites, may even appear to flare up to become brighter than any other sky object for a few seconds.
An unmanned free balloon shall refer to a freely drifting inflatable object which is driven with no power, is piloted by nobody, is lighter than air, and whose gross mass is more than 4 kilograms.
无人驾驶自由气球，是指无动力驱动、无人操纵、轻于空气、总质量大于4千克自由漂移的充气物体。
3
Presently a dark object was seen in the river, drifting towards us.