The twilight launch of a Minuteman II...

The twilight launch of a Minuteman II missile from Vandenberg Air Force base that threaded a glowing web of vapor through the sky Monday night enthralled Ventura County residents and prompted dozens of calls to local law enforcement agencies.

The missile, a reconfigured intercontinental ballistic missile, or ICBM, was shot out of a silo at 8:37 p.m., according to a spokesman at the Air Force base north of Lompoc. Ventura police and sheriff officials received a surge of calls soon after the launch.

“What you’re seeing is the sun reflecting on water droplets and unburned fuel propellant,” said Senior Master Sgt. Gordon Van Vleet, an Air Force spokesman. “Just as sometimes you’ll see a sunset that’s more beautiful than others, some of these launches leave a visible trail.”

Air Force officials notified mariners and aviators of the launch, warning them to stay out of the flight path of the missile, as well as the parts of the missile that would drop into the sea, Van Vleet said.

The missile, which was headed to the Marshall Islands, was part of a test to see whether the Air Force can launch objects into space to test sensor devices, Van Vleet said. The missile was designed to release nine target objects that will be tracked by another missile, the Santa Barbara County base said in a statement.

“From our end, it was a success,” Van Vleet said. “If the missile gets to the Marshall Islands and tracks the way it was supposed to, it will have been a success.”

The Air Force launched a similar missile in the early-morning hours earlier this month, Van Vleet said. The last twilight launch was in January, he said.