Reports of an unidentified flying object flowed in from observers in southern Africa and several islands in the Indian Ocean, NBC News reported Monday.
The sightings began about an hour after the SpaceX's Falcon 9 v1.1 rocket blasted off from Vandenberg Air Force Base for the first time Sunday morning.
One observer called it a "strange moonlike object."
The Falcon 9 was delivering Canada's Cassiope satellite to orbit, SpaceX said on its website.
A retired astronomer from Cape Town, South Africa, Greg Roberts, correctly identified the sight when he told The New Age the material visible was "propellant or rocket fuel" released by the Falcon 9 rocket's second stage.
After sending its payload into orbit, the Falcon's second stage jettisoned leftover fuel, a standard procedure to avoid burning up during re-entry into the atmosphere.