An eerie cloud that glowed briefly in the night sky Saturday was no UFO. It was created by humans — more specifically, a NASA rocket built to make clouds that shine at night.
The rocket launched as part of an experiment to create artificial noctilucent — or night-shining — clouds, the highest clouds on Earth. They naturally appear around 50 miles (80 kilometers) above Earth's high latitudes and are also known as polar mesospheric clouds.
Saturday night's rocket experiment lifted off at 7:46 p.m. ET from NASA's Wallops Flight Facility on Wallops Island, Va. It created a brief light show that was visible across the United States' East Coast and sparked calls from curious skywatchers as far away as Boston, according to the Associated Press.
"It was very impressive ... albeit short-lived," said Joe Rao, an instructor and guest lecturer at New York's Hayden Planetarium, who witnessed the event. Rao is also Space.com's skywatching columnist.
The experiment created a human-made noctilucent cloud using the fourth stage of a NASA Black Brant XII suborbital sounding rocket that spewed exhaust particles 173 miles (278 kilometers) above Earth. Ground-based radar and camera stations recorded the resulting cloud's formation and illumination. The U.S. Naval Research Laboratory and Department of Defense's Space Test Program oversaw the launch, which it called the Charged Aerosol Release Experiment.
NASA has observed naturally occurring night-shining clouds using its AIM satellite. The Naval Research Laboratory and Space Test Program used a satellite called STPSat-1 to observe Saturday night's artificial cloud.
"We weren't exactly sure what we were going to see, as this was the very first time that a noctilucent cloud experiment was attempted," Rao said. "Would it be something obvious to the eye, or something rather faint?"
The result, he reported, was spectacular.
Rao described the cloud as "a brilliant object" that displayed a wide, fan-shaped tail shortly after it was created. But the artificial phenomenon was over in just a few minutes.
"The 'head' of the comet (which was the rocket's fourth stage) rapidly faded out and the 'tail' gradually faded over the next minute or so into the background of the sky," Rao said.
Scientists will use the measurements of the artificial cloud to better understand natural noctilucent clouds, as well as help predict the effects of rocket engine exhaust in the upper atmosphere.
Saturday night's experiment was a cooperative effort by NASA, the Naval Research Laboratory, the Defense Department's Space Test Program and several universities. But the stunning cloud it created was seen by more than just the project's scientists.
"I'm sure many unsuspecting folks up and down the East Coast were surprised by this very unusual sight," Rao said.