Several Twitter users in France reported seeing a strange object in the sky on Thursday night, with some wondering if it might be a UFO (un ovni, in French).
It was seen above Le Mans in the northwest of France, and above Parisian suburbs.
One Twitter user joked that it was “holograms of Jean-Luc Mélenchon returning to their home planet”.
The left-wing Mr Mélenchon ran in this year’s presidential election but did not qualify for the second round, which takes place this Sunday (April 24) - and is known for using holograms in campaign meetings.
But Eric Lagadec, head of the French society of astronomy and astrophysics, confirmed late on Thursday that the object was actually part of a rocket from US company SpaceX.
This was confirmed by Spanish space website Frontera Espacial, after the glow was also observed over Spain.
"The second stage of a SpaceX Falcon 9 rocket was seen in the sky over Madrid," it reported.
“The 'cloud' was actually gases emitted by the engine brake to bring the object out of its orbit.”
It is brought out of orbit to cause this part of the rocket, superfluous after launch, to disintegrate in the atmosphere, to prevent it from littering Space.
SpaceX launched such a rocket on Thursday to place 53 Starlink satellites into orbit.
The launch took place from Florida at 19.51 Paris time.
Earlier this year, villagers living in Saint-Senier-sur-Beuvron, near Mont-Saint-Michel, Normandy, defeated plans by Elon Musk’s Starlink company to install a satellite base station with nine antennas.