Jeanie Liang is well accustomed to things that go boom in the night. Usually, the source is amateur fireworks or even gunshots as revelers menace the wooded area between her Creston Drive neighborhood and Interstate 280, where Stevens Creek snakes by. But the sound and accompanying percussion-like impact Liang experienced just after midnight Sunday was unique to anything she’s experienced before.
“It felt like something actually hit the side of the house,” Liang said.
From the vantage point of Liang’s home, it seemed the source originated from the northeast, somewhere around the interstate. Her family’s external surveillance camera faces the street, and it didn’t capture anything peculiar, but scores of other cameras – and ears – belonging to neighboring residents in Los Altos, Mountain View, Cupertino and Sunnyvale did: a flash of light followed by a powerful boom. In the early hours of the morning, residents of those cities took to social media to share what they witnessed and to search for an explanation. An explosion? A thunder clap? A blown transformer? A DeLorean traversing a wormhole?
Danielle Fujii of Sunnyvale’s Belleville neighborhood started a Nextdoor thread that attracted nearly 100 comments by Wednesday.
“It was so widespread,” she said in an interview with the Town Crier. “I’ve never seen anything like that before, the way it lit up the sky.”
The sound jostled and woke Barb Tolentino. A burst of light emanating from the direction of Fremont Avenue illuminated her home, located on Barton Drive in Sunnyvale near the Los Altos border.
“I was wondering if people had permanent hearing loss from it,” she said. “That’s how loud it felt.”
An external camera attached to Andrew Wu’s Sunnyvale home captured what appears to be a meteor, albeit one rising from the Earth rather than hurtling toward it. The sound follows approximately two seconds later. Wu lives on Samedra Street and his camera faces north, toward Los Altos.
Residents of Los Altos and Sunnyvale reported the incident to their respective police departments but neither agency was able to trace the source. And NASA Ames Protective Services staff indicated no sort of training or exercise had taken place at Moffett Field in Mountain View at the time.
A combination of physics, math and basic astronomy ultimately leads to the most plausible explanation.
Foothill College astronomy professor Geoff Mathews, Ph.D., analyzed Wu’s video Tuesday.
When meteors explode, they typically do so by the time they’ve dropped to an altitude of 10 miles, Mathews wrote in an email to the Town Crier.
Based on the two-second delay between the flash of light and the sound, and the knowledge that the speed of sound is approximately 350 meters a second, the object detonated an estimated 700 meters away from Wu’s camera, he said.
“It is true that a distant meteor flying towards the camera from over the horizon would similarly look like it is rising (there is a common phenomenon of people mistaking incoming airplanes and their contrails for rocket launches) ... but we know that this object was not distant, but close,” Mathews wrote.
The likely culprit, he concluded, was a firework. An exceptionally heavy-duty firework.
“My guess would be that it was a type used in community-level events (it looked and sounded similar to what I’ve experienced at fireworks shows),” he said. “If they were launching right over folks’ homes, that would be pretty rude!”
Note: It is illegal in California to possess “dangerous fireworks,” including firecrackers, Roman candles and sparklers more than 10 inches in length. Potential penalties include fines and a jail sentence of up to a year.