Strange light seen in Philly sky Tuesday night likely caused by rocket launch

Some people observing the night sky in Philadelphia on Tuesday spotted an unusual display of light glowing in the shape of a boomerang. The same pattern was observed in the night sky along much of the East Coast, prompting speculation about its source.

Photos and videos were shared on social media from Philadelphia to New Jersey to Vermont.

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The most likely explanation for the light is that it was caused by one of two rockets that were launched on Tuesday night. The European Space Agency launched the Ariane 6 rocket — a weather and climate observation satellite — from French Guiana around 8:37 p.m. Eastern Standard Time. And in Florida, at Cape Canaveral Space Force Station, United Launch Alliance sent its Vulcan rocket into space carrying experimental U.S. military satellites around 9 p.m.

Derrick Pitts, chief astronomer at the Franklin Institute, said Wednesday that he thinks the light seen in Philadelphia most likely corresponded to the European launch.

“Ariane 6, launched from French Guiana, was launched toward the north into a polar orbit — circling the planet north to south,” Pitts said. “So shortly after launch, it would’ve certainly been possible to see the rocket engine exhaust plume as the rocket sped north up along the East Coast but out over the western Atlantic Ocean.”

Pitts explained that many rocket launches send spacecraft east to catch additional momentum from Earth’s east-to-west momentum. Since the effect is greater closer to the equator, Florida’s Cape Canaveral is a preferred launch site in the United States. CBS News reported the Vulcan launch sent the spacecraft “arcing over the the Atlantic Ocean on an easterly trajectory” on its way to send a pair of satellites into orbit 22,300 miles above the equator. 

“Launching east from Florida, the rocket wouldn’t have been visible from all the way up here at 40 (degrees) North latitude,” Pitts said.

It’s also possible that ULA’s Vulcan launch followed a path heading up the East Coast first before traveling east over the Atlantic Ocean. That could explain the light patterns seen in the sky, as one meteorologist with the National Oceanic and Atmospheric Administration in Maine wrote on X. 

Regardless of which rocket caused the light pattern seen above Philly, it likely was visible because the rocket’s altitude was high enough to catch light from the setting sun. That light was reflected from particulates on the rocket’s exhaust, Pitts said, making it visible despite night having already fallen on the East Coast.

In areas in and around Florida, observing exhaust plumes from rocket launches is fairly common.

“SpaceX has already launched 100 rockets this year, many from the Space Coast in Florida,” Pitts said. “Night launches are so common there that inhabitants are used to seeing illuminated rocket exhaust. We up here in the Northeast rarely see exhaust plumes from night launches, so we’re surprised to the point of wild speculation.”

Anyone thinking the display last night was a UFO would be grasping at a more far-flung theory.

“If you think about it, it’s far more complicated and a way longer reach to suggest the phenomenon was extraterrestrial somehow,” Pitts said.