Late Wednesday evening, December 19, San Franciscans gazing out their windows saw something unusual in the darkened sky. It was a squiggle—bright, jagged, maybe a little unsettling. It looked almost like a question mark hanging in the air.
Some observers wondered if it had something to do with a rocket launch scheduled for earlier that day, or if it was flaming space junk reentering the atmosphere. Others thought it could be Santa, getting an early start, or aliens descending to ring in 2019 by annihilating us all.
Nope. The rocket launch had been canceled, and astronomers nixed the space junk theory. It appears to have been a meteor, whose “bright tail was visible for many minutes in the western sky,” the University of California’s Lick Observatory noted on Facebook. Sightings were also reported in Nevada and Oregon.
The meteor itself flashed by for just a second or so before it broke apart about 34 miles above the sea. But meteors can leave a few types of traces in the sky, according to the American Meteor Society. One is known as a train, comprised of ionized air molecules. Trains generally occur at least 65 miles up in the atmosphere, and may change shape as atmospheric winds blow. Smoke trails, on the other hand, are lower down, and more likely to be visible in the day. Sometimes smoke contributes to a phenomenon known as noctilucent clouds, which occur when water molecules form ice crystals in the smoke. The clouds resemble blue-green ripples dancing in a sunlit pool—or, maybe, a portal cracking open to another dimension.
This fireball left a lingering streak that was brightened by the way sunlight reflected off dust particles that persisted as the meteor fractured in the atmosphere, according to the Meteoroid Environment Office at NASA’s Marshall Space Flight Center. The center attributes the curious shape to the way that “upper atmosphere winds distorted the train over time, giving it a curvy, ‘corkscrew’ appearance.” Happy Holidays, though, aliens—wherever you are.