Many people snapped photos of the object and its spectacular plume and posted them on Facebook and Twitter. To the disappointment of UFO enthusiasts, the object was not an extraterrestrial coming to visit. Nor was it the star that led the three kings to Bethlehem after the birth of Jesus, as some who saw it suggested.

It was the Falcon 9 booster which took off from coastal Vandenberg Air Force Base carrying the latest batch of satellites for the U.S. company Iridium Communications.

The launch in the setting sun created a shining, billowing streak that was widely seen throughout Southern California and as far away as Phoenix.

Calls came into TV stations as far afield as San Diego, more than 200 miles south of the launch site.

Cars stopped on freeways in Los Angeles so drivers and passengers could take pictures and video.

SpaceX attempted to get the word out about the launch by tweeting about it about an hour before it was scheduled to take place. But not everyone heard the news, which compounded the confusion.

SpaceX founder and chief executive Elon Musk might have made matters worse with a tweet that appeared to joke about North Korean missiles.

"Nuclear alien UFO from North Korea," he tweeted in a reference to the rogue communist country that has regularly tested ballistic missiles despite international condemnation and sanctions.

The same rocket carried Iridium satellites into orbit in June. That time, the first stage landed on a floating platform in the Pacific Ocean. This time, the rocket was allowed to plunge into the water.

It was the 18th and final launch of 2017 for SpaceX, which has contracted to replace Iridium's system with 75 updated satellites. SpaceX has made four launches and expects to make several more to complete the job by mid-2018.

The satellites also carry payloads for global aircraft tracking and a ship-tracking service.

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