What made Wednesday night’s light show in the California sky so rare? Science explains it

Many UFO conspiracy theorists and laypersons alike probably had no idea what “noctilucent” meant until Wednesday’s phenomenon made them Google it.

Heck, even The Bee didn’t know. A quick-and-dirty search of our stories published online indicates we’d never used the word in a story, at least in the past decade or so, until Thursday morning.

From the Bay Area to Lake Tahoe, Northern Californians saw a strange light illuminating the sky around 6 p.m. Wednesday. It was unique and remarkable enough to prompt social media users to claim it was, of course, aliens.

Others speculated it must have had something to do with a couple of other astronomic events planned for that evening: a rocket launch from Vandenberg Air Force Base in Santa Barbara County was postponed — or was it, some pondered? Three astronauts also undocked from the International Space Station around the same time the light appeared.

The real, short answer: It was almost certainly a meteor, experts say. Boring.

But, as weather and space experts further explained, Wednesday’s meteor appears to have created something called a noctilucent cloud.

A 2016 post by NASA described noctilucent or “night-shining” clouds as “electric blue wisps that grow on the edge of space.” They can be seen from Earth’s surface and by astronauts on the ISS, NASA says.

They only form from 47 to 53 miles above Earth’s surface, in a region known as the mesopause. That small, 6-mile range is part of what makes them so rare, but meteors do often burn up in that part of the atmosphere.

“At these altitudes, water vapor can freeze into clouds of ice crystals,” part of NASA’s post reads. “When the sun is below the horizon and the ground is in darkness, these high clouds may still be illuminated, lending them their ethereal, ‘night shining’ qualities.”

Normally, noctilucent clouds form above polar regions - in which case NASA calls them polar mesopheric clouds - but can happen elsewhere. Meteor dust, for instance, gives a foundation upon which ice crystals can form and illuminate the night sky.

Though a bit crude and definitely not to scale, this illustration from the National Weather Service may offer the most efficient explanation of the phenomenon.

An illustration explaining noctilucent clouds. National Weather Service

UCLA climate scientist Daniel Swain tweeted Wednesday night that the light appeared to be an “unusually bright/large #meteor, which left a persistent ‘glowing’ trail known as a noctilucent cloud.

“Visible meteors are not that rare, but noctilucent trails are quite unusual!” he added.

The American Meteor Society on its website says it received 129 reports about a “fireball.” The society also received reports of a fireball over Minnesota earlier in the evening. As the NWS Bay Area forecast office notes, noctilucent clouds can be also observed after rocket launches. In October 2011, early-morning clouds that appeared to be blue and cirrus-shaped resulted from the launch of a National Polar-orbiting Operational Environmental Satellite System spacecraft from Vandenberg.

So those early theories that the light show had something to do with the scrapped Vandenberg launch may have ultimately been incorrect, but they weren’t totally out of left field.

Some Bay Area drivers captured video of the meteor burning up via dashcams.

The American Meteor Society said in a post that these videos of the fireball, which was also reportedly seen in parts of Nevada and Oregon, confirm it wasn’t a rocket.

“Both videos cleary (sic) show that it was a fireball and not a rocket launch as some people initially thought,” Vincent Perlerin of AMS wrote.

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