Sighting in La Ville-du-Bois, November 6, 2011

At around 1 p.m., a witness noticed an orange ball in the sky. It looked dull in colour and appeared about the size of a pinhead. It seemed to hang motionless at a great height, although the altitude was hard to judge. The witness looked away for a moment and could not find the object again. The sighting lasted about 10 seconds. No other witness account was collected.

The investigation put forward the explanation of an orange party balloon flying at roughly 500 m. Its apparent lack of movement can be explained in two ways. First, even a balloon drifting at the ground wind speed of 30 km/h would, seen from 500 m, move at an angular speed of about 1° per second, which the human eye has trouble detecting against a uniform sky near the zenith. Second, the wind at 500 m is not always the same as at ground level. Helium-filled balloons usually burst fairly quickly as they climb, so the sudden disappearance of this one was entirely normal. The case was therefore classified B: probable balloon.