Really really big.

After my post identifying the Falcon 9 propellant cloud as the UFO that was seen over much of the Indian Ocean, I received a few further emails.

Devin Edmonds sent me links to a couple more photos people had posted to Facebook. One of the clearest was by Tsiaro Ryan'Avo probably taken from Madagascar:

It shows much less motion blur than many of the photos of the propellant cloud, so I hoped that it would be possible to identify the stars in it and from that figure out how big the cloud was.

I submitted the image to nova.astrometry.net which can analyze an image and automatically figure out where in the sky the camera was pointing. It gave this cool output:

It also gave a KML file as the output, which I opened in Google Earth. There I measured the height and width of the cloud and converted it from RA/Dec to degrees. The average value was 6.672 degrees. For comparison, the moon averages 0.528 degrees in width as seen from the ground, meaning that the Falcon 9’s propellant cloud was more than 12 times as wide as the full moon! No wonder so many superstitious people thought that the world was ending.

From one of the images I showed in the prior post about this, we know that the rocket stage was about 1495km above sea level when it flew over Madagascar. With that distance and the angular diameter of the cloud, we can do some trig and calculate how big the cloud was in space.

The kind of amazing answer: 174 kilometers (108 miles) wide! Really big; Réunion, where it was seen from, is only 63 kilometers long. Madagascar’s widest east-west width is 560km, so the cloud was almost a third as wide as Madagascar.

I hope planetary nebula scientists have looked at the results, as this was likely the largest nebula simulation to be photographed in recent years.

The Helix Planetary Nebula, NGC 7293, for comparison.