This one is well documented. The Los Angeles sky on the evening of December 22, 2017 was lit up by a SpaceX Falcon 9 carrying ten Iridium satellites, launched from Vandenberg about 210 km northwest at 5:27 PM. The rocket was still in sunlight high above the ground after the sun had set below the horizon, and that is what made its exhaust glow into the cloud shape people described. The launch record and the timing line up closely with the sighting, and the direction matches too. The next most likely idea, a bright star such as Vega twinkling near the horizon, scored lower because it doesn't explain the expanding cloud. Drones and aircraft fit poorly. Overcast weather makes the picture harder to confirm from the sky itself, but the launch evidence carries most of the weight here.
From the archive · #t67xuv836hbz
Glowing plume over Los Angeles after sunset: the Iridium-4 Falcon 9
Rocket, not RoswellWant answers like this first in Google? Add WTH Was That? as a preferred source.
Sky Snapshot 5:35 PM, give or take 15 minutes
- Sky
- nautical twilight
- Moon
- waxing crescent, 32° up
- Planets up
- none bright
- Bright stars
- Vega (northwest 29°), Capella (northeast 29°), Rigel (east 3°), Betelgeuse (east 3°)
- Weather
- overcast, wind 6 km/h
- Space weather
- quiet (Kp 2.7)
- Sunset
- 4:48 PM
Download the snapshot card to share it anywhere.
What people saw
- When
- Dec 22, 2017, 5:35 PM PST
- Where
- Los Angeles, California, US
- Looking
- northwest, low in the sky
- Lasted
- 5 minutes
- Looked like
- one, white/blue, cloud, rising, with a trail
- Sound
- none
Right after sunset on December 22, 2017, a bright point of light with a huge, glowing, expanding cloud behind it climbed over Southern California. Traffic slowed on the freeways, the Los Angeles Fire Department got calls about a "mysterious light in the sky", and people as far away as Phoenix and San Diego saw it.
It was a SpaceX Falcon 9 carrying ten Iridium satellites, launched from Vandenberg about 210 km to the northwest at 5:27 PM. The Sun had already set for people on the ground, but it was still shining on the exhaust high above them, which is what made the plume glow.
Sources:
https://www.nbcnews.com/news/us-news/spacex-rocket-lights-sky-it-carries-satellites-california-n832301
https://laist.com/news/kpcc-archive/what-s-that-flying-over-los-angeles-a-spacex-rocke
From above the area, the way they looked, and what was overhead
The map needs JavaScript. The checks below list everything it shows.
The circle is the area the report came from, rounded to about 10 km. We never show a witness's exact spot.
See it in 3D on the Sky Globe, at the moment it was seen
What it could be
-
Rocket launch Likely100%
- +40Falcon 9 Full Thrust | Iridium-4 launched from Space Launch Complex 4E, Vandenberg SFB, CA, USA 227 km away, 7 minutes before your sighting.
- +15Timing and twilight are right for a glowing "jellyfish" exhaust plume.
- +10Close enough to see the rocket itself climbing.
- +15The pad is toward the NW, where you were looking.
- +15A glowing cloud, cone or trail is the launch plume.
- +15Rising motion fits a launch.
- +5Plumes stay visible for minutes.
-
Bright star (twinkling) Possible66%
- +25Vega (magnitude 0.03) was 29° up in that direction.
- +15Low bright stars flash red, green and blue through turbulent air.
- +8Twinkling is strongest near the horizon.
- +10Stays for a long time.
-
Drone Possible50%
- +10Consumer drones carry small red, green and white LEDs.
- +10Drones fly low.
- +10Flight times of a few minutes fit.
-
Satellite (ISS or another bright one) Doesn't fit33%
- ·Satellite passes couldn't be checked (orbit data was unavailable).
- +8The duration fits a pass.
-
Aircraft Doesn't fit30%
- +10The duration fits.
- -10No blinking and no sound is unusual for an aircraft, unless it was far away.
- ·Flight tracks weren't checked: aircraft are only looked up live, for reports filed within a few minutes.
-
Balloon Doesn't fit28%
- +15Silver or white and shiny fits a foil or party balloon.
- +20Drifts with the wind.
- +10Stays in view for minutes.
- -25Balloons don't leave a trail or look like a streak.
What we checked
- Satellites: not checked (orbit data missing)
- Starlink trains: not checked
- Launches: Falcon 9 Full Thrust | Iridium-4, 227 km away
- Aircraft: not checked (no flight history feed yet)
- Planets and Moon: no bright planets up, and the Moon was up
- Space weather: quiet (Kp 2.7)
- Weather: overcast
- Meteor showers: Ursids (peak)
Launch page: Iridium-4, with every city that could see it.
How we worked this out
We took a snapshot of the sky from 15 minutes before to 15 minutes after Dec 23, 2017, 1:35 AM UTC at 34.05, -118.24, and scored 19 possible explanations. Each one starts from how common it is, then gains or loses points for every detail the witness gave and every record we found. The points are listed next to each reason above. "Likely" means 80% or more and "Possible" means 50 to 79%. Anything lower doesn't fit, and if nothing reaches 50%, the case stays unexplained.
Sources: launch schedule from Launch Library 2; planetary Kp from GFZ Potsdam; weather from Open-Meteo; Sun, Moon and planet positions worked out on our server with astronomy-engine. Engine 0.4.0, snapshot v2, worked out Oct 29, 2026, 4:52 PM UTC.
Not available for this report: satellite passes.
Discussion 0 replies
This reply only uses the sky checks above, so it can't claim more than the data shows. Was it helpful?
