Local media across the US began receiving reports and video footage of what appeared to be, and sounded like, aircraft flying in formation. However, the sheer size of the visible phenomenon fuelled wild speculation online.
Theories ranged from military planes, presumed to be C-17s or C-130s, flying in formation, to UFOs and even suggestions that Santa's elves were doing some preliminary reconnaissance before the big night on December 24.
"When we first noticed the formation it was horizontally stretched out, then it seemed to hover over the lake in front of our house, and then it flew in a vertical line directly over our house. Interesting but very strange to say the least," Marci Arant, a South Carolina resident, told RT.com. "My 10 year old was worried we may be getting bombed."
The unidentified lights seemed to be flying in a westerly direction, fuelling speculation that they might be aircraft forming part of relief efforts for beleaguered California that has been scorched by a series of intense wildfires in recent days.
Denver's South Metro Fire Department spokesperson Eric Hurst uploaded security camera footage from outside his home which captures the full extent of the formation.
Comment: Hurst has since taken his video down, apparently to share it only with Fake News outlets. Bad idea, as you'll see in the following 'news' report about it, which brought in an 'expert' to tell us what it is (he doesn't know - he's passing off a guess as 'knowledge')...
"Strange lights recorded on our roof mounted Nest camera in Littleton which faces northwest. The lights moved from east to west starting at 8:55 p.m. These are possibly a military C-17 formation," Hurst wrote.
The FAA, Shaw Air Force Base, McEntire Joint National Guard Base, Columbia Metropolitan Airport all denied any knowledge of or involvement in the puzzling shenanigans.
Comment: Update 20 Dec 2017
These could have been aircraft of some kind, but they were either - depending on eyewitness reports - completely or unusually silent. Given that there's no official involvement, the plane angle means they must be part of some sort of 'top secret' operations. But then why give away their presence with bright flashy lights and a striking visual formation?
Here's another interesting video captured by a Denver resident who claims the string of lights was preceded by an 'asteroid' (by which he probably means a meteor fireball):
Here's how the video uploader described what he saw (and no, to him also, they weren't planes): One possible match for this fireball report is logged on the American Meteor Society as having occurred at 03:32 UTC on December 10th, which corresponds to 20:32 local time on December 9th. Here's video footage of that fireball as seen from Broken Arrow, Oklahoma.
Weird!